Motor advice: what to get?

[Dustfinger]

My team and I are building a 15 lb robot for a battlebots competition but need help finding some good motors. The ideal motors would b 12v, at the most 1.5 lbs, run between 500 and 800 rpm's, are at most 3.5 inches wide and at most 5 inches deep. These will be carrying around the entire robot so the need to be good. If anyone has any info. on some motors like this or very close to it, or knows of a place where I might get some, please post.

P.S. I've tried robot market place.