Is it possible a Walmart manager put that ammo there so he would have some for a customer that buys a gun? Rural King does that. They say they have no ammo, then when you buy the gun and ask again, amazingly they have a box hidden under the counter. It happened to me last summer when I bought a 9mm from them.
Walmarts in the Metro Indy area don't sell guns, and still rarely have any. I got super lucky the day after BrassBadger was announced on here and picked up 3 bulk packs at the WM down the street, so I am set for this year, but haven't seen any more since (trying to find some for my dad as well).