www.sandmountainherbs.com/ground_nut.html they have them in stock and for sale. http://www.localharvest.org/store/M16074 shows a listing for MoonBranch Botanicals in North Carolina that has them.
Toni I just put an order in with Sand Mountain. I suspect (but do not know) that their stocks of tuber are thin. Some years I gets some, others I don't. I DO shop off the bottom of the market, and they are the deal.