What cartridges (and bullet weights) would most likely be found in a Western US (NM, WY, CO, etc...) town?

anything flat shooting: 270, 280, 7mag, any magnum probably. I can't imagine any store that sells rifles not having a 30.06.

Bullet wts will include most per caliber.

While in Casper the last 3 antelope seasons, I spoke with many of those who work for Game and Fish there and the most popular caliber for them was the 270 Win hands down. The 160 partition was the bullet of choice for most I spoke with, as this was their "do-all" rifle, elk-moose on down.

Depends on the size of the town. In most large gun shops you will find almost any factory loading you would want.

If you can find a Wal-Mart just about anything in the standard calibers can be found. IE .243, .25-06, .270, .280, .30-30, .308,.30-06, 7mm Mag, .300 Win Mag, .338 Win Mag, plus most of the WSM's and WSSM's. At the small hardware stores and mom & pop's you can limit your cartridges to .243, .25-06, .270, .30-30, .308,.30-06, 7mm Mag, and .300 Win Mag. Just don't come out here with a big ol Weatherby Mag and hope to find ammo in a small town.