I bet they stop selling ammo altogether in the urban stores. They already don't sell anything more than BB/paintball/airsoft at the walmart in my city. Have to drive to the country walmart to buy real guns.
Where do you live?
AFAIK every single Walmart in my area has ammo, although some have more than others. This includes a local store that was given a total renovation and reopened about 9mos ago. All of the stores seem to sell a LOT of it and IMHO it would be foolish for them to take it out.
That said, AFAIK only two DFW area Walmarts sell guns, and they're located at opposite extremities of the metroplex- one in a far NE suburb, the other in a far SW suburb, probably ~40mi from one another. Despite this, you can drive 60mi north, and both the Sherman, TX and Denison, TX Walmarts have guns, despite only being ~6mi apart!