Is it possible to obtain uncut sheets of cards from Arkham Horror? I am planning a tournament for a major board game convention in southern California for February and am looking for maybe rare or hard to find paraphernalia for such an event.

You should probably try to contact customer support with such questions.

I was more or less trying to get ideas for prizes. :/

Well, the only exclusive Arkham material I know of are the AOs from Arkham Nights and the cards that can be sent for if you buy the novels. If you have any of these and you're willing to part with them, they might work. But honestly, I'm not sure that going with Arkham Horror material for prizes is the best idea. The winners are probably going to be quite experienced with and enamored of the game, which means they will probably have everything already, possibly even the promos.