... You mentioned USI, too. I can't recall what the acronym stood for, but they made the USI Destroyer (a potato-cannon style bazooka) and what was the other one... the Patriot? An inline blowback similar to the Model 98, but had a regulator at the back end like an Automag.
I think they had a pump, too...
And, that same inline design was later used in the Mirage, another one of those companies I can't recall the name of the manufacturer.
And speaking of pumps, there was the TM-11A, the Razorback, the Outlaw, the Wintec, and the NW-89 and NW-90. Gimme a little while and I might be able to recall the makers of each of those, but feel free to pipe up in the meantime.
Who was the shop that did the "Tip-n'-Strip" mod for the 68 Special? How about the guy that made the "Frank Guns"? Or the brass PGP-based Anhiliator? (There was also an Obliterator.)
Ah, RebLine is another- started out making Nelson upgrades, eventually made a whole Nelson clone (including one in solid brass, complete with silencer, in a fitted attache case.)