My local WalMart has a pretty good stock of rifle and shotgun ammo.
As said, handgun ammo is hit or miss but IS out there. I've noticed that Wal-Mart seems to be able to keep a reasonable handle on 380 auto and 44 magnum. I also see 45 ACP and 45 Colt from time to time. I've been able to buy several boxes of 38 special and .357 magnum at Wal-Mart in the past couple of months, but probably only find it on one out of every ten trips or so(and usually then only when it has just been put out). .357 sig turns up every once in a while, and seems to stick around for a little while when it does. I haven't seen any 9mm in Wal-Mart since the week before the Newtown shooting.
The local gun shops around here seem to have a more reliable stock than Wal-Mart, and almost have 38 special and 357 Magnum when I go in. They may not have the brands or bullet weights I necessarily prefer, but do at least have something. I don't always ask about 9mm(I don't own one, but have several regular shooting partners who do) and they have it about half the time.
.22LR and .223 Remington/5.56 NATO are non-existent around here. Even .22 shorts, .22 longs, and .22 magnums are thin, but can usually be found with looking.