It can depend on the economy of a town and also how often you are shopping there for a particular item. Your best bet for really good items is outside Fairfax where all the posh people mill about - sleep for a few days or travel about a while and then at some point, the shops and vendors should restock and the decent stuff will turn up.
Failing that, see if someone will perhaps trade you a turret pistol on XBL.
Thank you, I shop pretty much exclusively in Bowerstone, but I'll try Fairfax.
XBL is out atm
I guess I'm still pretty early into the game, but I'm getting some other good steel stuff, so hoping for a turret pistol soon.