If you are asking about C. henryi, they are very difficult to find for sale. I would ask in a few of the facebook groups that exist. Perfect circle did sell them at one time (at least the seed), but I checked their website and they do not have it listed.
Crazy to me the industry pushes Chinese chestnut as hard as they do and not the Chinese chinquapin. In my opinion they are way more versatile for wildlife. I have a few seeds I got off my bushes this year so might have to just keep growing my own.
I’ll try the Facebook group idea also. Hadn’t thought of that