Ebay is your best bet. You may be able to find one now and then on some of the "for sale" forums here at AT or HardOCP and the like.
Have you checked the board for bad caps? It's reasonably likely that's your problem.
Here's the story about it. If you do have bad caps you can send the board the Abit along with $25 and they'll fix it, or you can fix it yourelf or have someone who knows about this kind of thing fix it for you.
Here's a guy who can replace the caps for you, I've had him do a few Abit boards for me and he's done a great job.