The question of how is the best way to hire “artists to provide graphics, music, and other artwork for Open Source projects?” was posed the other day on http://slashdot.org well one was is to hunt them down on http://rentacoder.com or http://www.newstoday.com but very likely you will get all sorts, I would recommend nicely hunting down talent through online communities, artists blogs and websites
http://ask.slashdot.org/article.pl?sid=04/06/22/217250&mode=thread&tid=141&tid=152&tid=185&tid=188