The gunslingers will come through with the clothes on their back, and whatever supplies they have on them. Once their ammo runs out, they will either need to come up with a way to purchase the materials they need to make more, or find a way to buy bullets. Unlike Roland, the gunslingers are not going to have guides to help them in the present, they're either going to have to make friends or wing it. 

There's a few ways that thing can work, but for now I'm kind of testing the waters to see if I get any interest before I go into the finer details.