The Wal-Mart that I usually visit here in Middle Tennessee carries both Guns (a few Shotguns and .22 Rifles, I believe) and Ammo.
I think all of the Wal-Mart stores in this area have Guns and Ammo.

They seem to have a hard time keeping Ammo in stock here. The ammo showcase is usually more than half empty, and they always have a "2 box limit" on Ammo purchases.