I waited for like 5 days and they still haven't resupplied. Gun runners is where I get all my ammo. Also I just got done with the DLC could that be the problem?

Try this:

Save near the vendor.
Exit and restart the game.
Load up the save.

This should force resupply the vendor because whenever you load up a save game, the day gets reset to Sunday and Sunday is one of the days when vendors respawn.

on my copy, there are several merchants that won't restock. it is a pain to save and quit and reload.

That worked thanks...yea I can't get the one in Crimson Caravavn Company to resupply