All the artists I know that work with that kind of stuff mostly do NSFW type art, knocks out a few people as it's a licensed/trademarked character. Then again, I don't think I have seen Casper nor a horse wearing any pants.
Typically you find an artist by checking out their portfolio and seeing if they have a style you want. You then hire them and dial in the details of what you want done, revisions, etc. Having people make art for you to then decide on isn't worth the time of the artist as there is no commitment to pay. It's like when companies do design contests, the only winner is the company.
