The Knight's Honor Achievement is the second rarest achievement in DSR, only behind the Dark Soul (get all achievements). So it can be argued it is the hardest one to accomplish, as you need to play through the game 2.5 times and search every nook and cranny. This guide will hopefully lower the amount of pain caused by the deep dive you have to do.

All boss souls are needed to gain all unique weapons, and all boss souls (except DLC) have at least two weapons to ascend to. The boss souls needed are; Moonlight Butterfly (2x), for the Crystal Ring Shield and the Moonlight Butterfly Horn, Quelaag (2x), for the Chaos Blade and Quelaag's Furysword, Iron Golem (2x) for the Dragon Bone Fist and the Golem Axe, O&S (2x, one from each) for the Dragonslayer Spear and Smough's Hammer (note; easiest to fight Super Smough in NG and Super Ornstein in NG+ imo), Sif (3x), for the Greatsword of Artorias (cursed and non cursed) and the Greatshield of Artorias (in NG++ can just rush Sif and continue to Anor Londo normally), Gwyndolin (2x), for the Tin Darkmoon Catalyst and the Darkmoon bow, Priscilla (1x) for the Lifehunt Scythe, and Gywn (1x) for the Greatlord's Greatsword. You do NOT need any DLC weapons for the achievement, even in the remastered version.

To ascend a boss soul, you have to have a +10 version of the respective weapon type (e.g for Darkmoon Bow, you combine a +10 bow (any kind) and the soul of Gywndolin). All boss soul ascension is done by the Giant Blacksmith.

The total count of +10 weapons is; 1 fist weapon (Caestus from Andre), 2 thrusting weapons (can revert lightning spear from Sen's Fortress mimic in both NG and NG+), 1 axe (Battle Axe from Andre), 1 catalyst (sorcerer's catalyst in Lower Undead Burg, need Residence Key from Undead Merchant), 1 curved sword (revert enchanted falchion from Duke's Archives mimic),1 bow (short bow from Undead Merchant), 1 hammer (club from Undead Merchant), 1 katana (Uchigatana- kill Undead Merchant after buying what you need), 1 halberd (halberd in Undead Parish), 2 non broken swords (longsword from Andre), 2 shields (tower kite shield from Andre), and 1 broken sword weapon (start game with straight sword hilt).

Roped in the Boss Soul section will also be Tail weapons (i.e weapons you get from cutting off tails). Best for UGS or similarly high DPH weapons and builds (sorcery is also good w/ soul spears)

Gargoyle Tail Axe- Easiest if you focus getting behind the first Gargoyle before the second Gargoyle spawns. Easy to get behind it, straightforward enough.

Drake Sword- From the Bridge Wyvern. The easiest way to get this is to shoot a bunch of arrows at his tail from under the bridge.

Dragon Greatsword- From the Ancient Dragon in Ash Lake. This is accessed on the opposite side of Blighttown from Quelaag's arena, by rolling through two illusory walls and making your way down the Great Hollow. Walk behind the dragon at the very end of Ash Lake (watch out for the Hydra- you can abuse quit outs to get by him) and whack his tail. NOTE: DO THIS AFTER GETTING THE LORDVESSEL. GETTING OUT OF THE GREAT HOLLOW SUCKS.

Priscilla's Dagger- From Priscilla in the Painted World. Super easy because she stands still until you attack her. Just walk behind and do the most damage you can in one hit and it should come off.

Dragon King Greataxe- From the Gaping Dragon in the Depths. Attack close to the base of the tail, easy to get around the boss when his mouth is on the ground.

Moonlight Greatsword- by far the most annoying tail to get imo. From Seath the Scaleless' biggest tail, you have to stick to his ass and hope he doesn't use his tail slam. Attack the tip of the tail.

On top of boss weapons, you will need to farm some normal enemies for rare equipment. This ranges from guaranteed drops to >1% chances, but with the right setup it can be more easily done.

Farming Setup
The easiest way to get the max item discovery (410) is with 10 soft humanity and the Covetous Gold Serpent Ring, found in Sen's Fortress. Being hollow or human doesn't affect item discovery. In my experience, 410 raises the drop chance about 3x. The percentages for each listed drop are going to be assuming 0 item discovery though.

Black Knight Equipment
The entire set of Black Knight equipment (barring the armor set) is required for the achievement. The only place to farm Black Knights is in the Kiln of the First Flame, after filling the Lordvessel. Each weapon has a 20% chance to drop from its respective knight, and the shield has a 5% chance from any of them.

Silver Knight Equipment
The weapons of Silver Knights are necessary as well. The knights can be found scattered through the final section of Anor Londo, and the drop chances are as follows; 1% for the shield, 2% for the spear/sword from their respecitve knights.

Stone Equipment
The stone greatshield (2%) must be farmed from Stone Knights in the Darkroot Garden (right before Moonlight Butterfly Arena) but the greatsword (2%) can be purchased from Shiva of the East in Blighttown. You have to be a member of the Forest Hunters Covenant, accessed from Alvina the cat. She will be behind the Crest of Artorias door and sitting on a ledge in a building directly ahead.

Demon Spear
Actually a pretty fun weapon in PVP, I don't see it very often. Can drop from the Bat Wing Demons of daytime Anor Londo with a 2% chance. Or, this weapon can also be bought from Shiva in Blighttown.

Crest Shield
Guaranteed drop from Oscar of Astora when revisiting the Undead Asylum. If you go up the Undead Parish elevator from Firelink, there will be an opening behind you. Walk off of the elevator onto the roof, and make your way along the right edge until you can roll onto the protruding column. Then walk up the stairs and curl up in the crow's nest. The bird will take you back to the Undead Asylum (be patient, it takes a while) and Oscar will be where he gave you the Estus Flask.

Sanctus and Grant
Paladin Leeroy's equipment can be looted from his phantom after he invades you in the Tomb of the Giants. The requirements of him invading are; the Lordvessel has been placed, Nito is still alive, and you are human. In the Tomb of the Giants, once you have left the dark area and can see Ash Lake, walk to the very end of the ledge before the hallway to the Pinwheel room. He will invade soon after you reach the cliff.

Crescent Axe
The two ways to get this are 1) Kill Patches (it doesn't matter which encounter, he'll always drop it) or to complete his small questline and purchase it from him. When you meet him in the Tomb of the Giants, talk to him and tell him you are NOT a cleric. If you select yes he will become hostile later. Then you let him kick you down the cliff. After you climb out, talk to him and he will apologize. Forgive him. After you kill Nito, he will appear in Firelink as a merchant, where the Crescent Axe will be in his inventory.

Channeler's Trident
Can be dropped with a 1% chance from any Channeler (Undead Parish, The Depths, Duke's Archives) but only the Channelers in the Duke's Archives respawn. It took me an ungodly amount of time to get one so good luck.

The easiest section b/c everything is guaranteed to be in the same spot and you don't have to kill a boss for it. Also surprisingly few weapons fall under this category.

Astora's Straight Sword and Dragon Crest Shield
Found in the Valley of Drakes, by the Undead Dragon's right hand. If you pick both of these up he will wake up, so grab them and quickly run away.

Black Iron Greatshield
Located on Iron Tarkus' corpse (RIP a real one) directly left of the entrance to the Painted World. The bottom of the Anor Londo church is accessed from the huge, moving spiral staircase.

Bloodshield
Found in the Painted World, in front of the second Undead Dragon. Fun fact: if you kill the Undead Dragon's torso and then walk down to where its legs are, you can jumping attack them and they will raise in the air for some reason. If you fall down where the legs were blocking boom you just skipped half of the Painted World.

Dragonslayer Greatbow
From O&S boss room, walk up the staircase on the right, past the Giant Blacksmith. Keep hugging the wall until you reach a broken window. Fall through and follow the path to the bow.

Dragon Tooth and Havel's Greatshield
In the Anor Londo bonfire where Solaire hangs out before O&S are killed, walk left out of the room towards and past the staircase. Enter the room on the left, with nothing but a bunch of tables and a fireplace. Roll into the fireplace (illusory wall) and loot all the chests. Note: The chest standing alone is a mimic.

Velka's Rapier
Requires the Annex Key from the maze below the courtyard. Found on a corpse a little after the Annex door. Knock down some wooden boards by rolling.

Effigy Shield
From the second bonfire in the Tomb of the Giants, backtrack just a little bit and go down one of the paths. To be honest I'm not 100% sure where it is but if you go back from the second bonfire you'll find it. Just be thorough.

That's all the weapons. Congrats, you are now a god gamer. Some of those weapons have really cool movesets and some are just kinda OP. Have fun.