Walmart does not have a no gun policy and their corporate HQ has been very explicit in their stance. Their stores operate under local law and, if it's legal to carry outside the store it is legal inside the store. I've seen people OC'ing in my local Walmart, with no hassles at all. They sell ammo, too. So does my local Meijer, where I've carried many times. And seen a few folks OC'ing there, too.
Well good, maybe they changed their tunes. The Franklin Walmart used to have the handgun with a line through it sign posted in the front of the store. Is that gone now? They quit selling guns there (rifles and shotguns....they never sold pistols) a few years ago.