Also... at the end of the day, personal scale combat in Gearhead has, I think, always been intended to be a bit on the 'realistic' side (martial arts aside). That means that just about anyone with a saturday night special from the local weapon shop is a threat, and it really doesn't fit with super-secret legendary guns that you pull from a stone and anvil or whatever.
I mean, look, you shoot someone in the head with a plasma cannon, they die. What more do you want? Do you want a gun that makes them MORE dead? Maybe a gun that shoots them for you, then cleans up afterwards and offers you a nice cup of hot chocolate to get over the sniffles?
I think that factions and so forth could maybe offer fancy custom guns and such, but I can't really see them as being substantially stronger than the stuff available midway through the game. Mechs are huge expensive military hardware with generally limited production, so it stands to reason that the best would be hard to get. The best all-around firearm in the world, on the other hand, rolls off its conveyor belt a million units at a time and is given to the soldiers of every military in the solar system as standard equipment. I mean, what are they going to say to their boss when the entire squad gets killed? "Oh, yeah, it sure is a pity they all died, but I really couldn't let them have the laser pulse pistols... they were only faction rank 5! They should've spent more time doing minor quests, then we'd have been able to distribute the pulse pistols and would've won. Pity, that."