I've seen that ammunition I want to buy is always unavailable or some super-duper-extreme-shock-terrorist ammo that costs an arm and a trauma plate to buy.
For instance:
Christmas = .32 Automatic. Do they have .32 ACP? One box of FMJ. Two boxes of high-priced JHP/HP rounds.
More recently: Wanting a .38 Smith Model 10-5.
Any .38? Some, yes... overpriced 'cowboy loads'. No LRN/FMJ, non +p stuff on the shelf. But I spot three or four boxes of .32 ACP - this is only natural, as the .32's firing pin is currently broken.
Ammunition shortages are geared towards whatever caliber you most want to get.