The internet is full of free resources, and you can learn how to make graphics online as well. Or put a post out on Craigslist offering a % of the revenue.
It is going to be hard to get someone to do the graphics for free. Unless they see something genuine in your game and want it for their portfolio or something like that.
Comments
However, there are some options;
http://opengameart.org/
http://sandbox.yoyogames.com/make/resources (has many links to free resources)
Hope that helps!