It depends on what you mean by computer art. Do you need pixels, sketches, 3D art or a finished piece? Also, you should list what you are willing to pay. I'd be willing to do a piece, but it depends on how much you want to pay.
Iron Mosquito is right: I'm sorry, but I doubt you are going to find an artists who is willing to do something for free. Most artists have jobs outside of their art and their time is justifiably valuable.
I suggest you look around on the internet for an artist you think is good, check their pricing, and try to find out if they have a good reputation.