Found info on a weapons related site www.weaponsguild.com concerning buying ammo at walmart.
It seems the stores put out ammo at 7am on the day after it's received.
You can search for local availability on walmart's web site.
It will show you what is in stock and it will show up as soon as the shipment hits the stores prior to it being shelved.
So check for ammo availability early in the morning and get there before 7am.
I'm finding good availability of 7.62x39 steel cased ammo locally (used by the SKS and AK-47 semi-automatic rifles)
I had to search www.walmart.com and try several different home stores to find the ammo.
Try searching for .22 or .223