The two stores that I was in a lot during the ammo shortage the most - a Walmart and a local Farm supply store [decent firearm/hunting section]:
.40 S&W was more available than 9 mm and 9 mm was more available than .45
.44 magnum was always available.
.357 and .38 special was generally available.
.22 was always around - not necessarily the brands I liked.
If you want something that is always around? .44 mag or .22.
But - I would go with a .40 or 9mm.