OK well believe it or not there were only about three MATX boards available on X79 and each one is as rare as hen's teeth. The full sized boards are hard enough to get hold of, and go for stupid prices because there are cheap 8 core Sandy and Ivy Xeons out there that run in them.
The last board I sold (Gigabyte X79 UD3 rev 2, the decent one) went for £150. I paid £58 for it on a clearout from Amazon ages ago.
The problem is that because Intel move through tech like crap through a goose they ditch the older tech fast. So that's literally it, and you can't get them any more. Unlike 775 which lasted for years and was so popular you could still buy brand new boards until recently. Now? a chipset will literally die on its ass and vanish.