Although it would be nice to see all the slot and room keys in one category, if you're looking to bid, you would still have to search the general casino category as most sellers don't look at the fine breakdowns when they decide where to list. There is already a category under CASINO called CARDS. I'm pretty sure they had playing cards in mind when they created it, but it's general enough to include playing, slot club, and room key cards.

There's also a category under POP CULTURE where you find trading cards and such. That's where the credit card and telephone card collectors seem to list. When I've sold slot club cards, I have dually listed there and in the CASINO general category.