Any Chestnut trees sold in North America are almost certainly going to be cultivars of Old World species, typically the Chinese chestnut. I've heard of efforts to produce a Chinese-American hybrid with resistance to the blight, but for now, we're stuck with Chinese chestnuts for the most part. I've been fortunate enough to see some isolated individuals in secluded parts of the Appalachians where native chestnuts still live, so they're still out there.