Several material suppliers set up booths at the Blade Show in Atlanta in June.

One of the bigger setups is Masecraft, they also have a website: https://www.masecraftsupply.com/Stabilized-Woods_c_334.html?viewall=1

Keep in mind that when you submit blocks to the shop, there are specific dimensions (with a range), depending on which knife you want built.

If you go through a dealer, they can walk you through the size requirements. In the Randall ordering questions" thread the sizing sheet on Randall letterhead was posted (several times, actually). As soon as I find the specific post I'll update this one.

(edit) ah, here we go: http://www.knifetalkforums.com/ubbthreads.php?ubb=showflat&Number=131092#Post131092