For items to be displayeble, game has to be approved by steam.

These restrictions were placed upon creators because lots of them made games that were "spam" games, made just for the steam items service, with the goal of spawning, spamming and mass selling lots of items to players be it through private means, through their in game store or making the items dropable and getting a cut when players sell them on steam market.

If this game reaches enough sales and player time, it will be approved too, so best you can do is spend some money, leave it running in the background and hope for the best.
Hope that helps