One thing you might try is DeviantArt... see if you can get some artists to contribute to the game for free (or deferred compensation) for credits.
In the photography world is very common for photographers to shoot models for free in exchange for portfolio images. It's a win win for both. The photographer builds his portfolio and experience working with live models and the model gets some free professional quality shots to build up their own as well as practicing modelling, getting over fear, etc.