You could try Randy at the NRCS of Fannin County. He's probably got some info on bentonite and that's not too far from you. I can send you his email address in a PM if your interested.

Word of caution though, Randy doesn't recommend the stuff! He told me he's never seen it work. You may ask that question on this forum. "Does bentonite work?" Ask for specific examples from people before you buy a large truck load of the stuff. It's expensive and you'd better know what you're getting, as far as the practicle results go.

Good luck!

0.6 acre pond / 13' max depth / Bonham, TX