1:The tommy gun thing is more for flavor that realism, but it's there, not much that can be done about it, so i just suggested a change. also it's iconic enough that any surviving models would be a good prize to offer a hit man, even if just to mount on his wall.
2: The grease gun probably would survive in a army storage building, at least enough of them to arm a few groups of soldiers, also, it's cheap, and blue prints for it would be something the public would have been able to get their hands on since it's so old, it wasn't even close to new, so after-war models could exist.
3: The P90c isn't the real life P90, it looks like a police model made in 10mm for the US law enforcement groups, FBI, ATF, swat teams, etc.
4: Retooling guns for NPC usage is a bad idea, it sucked in FO3, and it would suck in FOnline, if you're going to have something drop loot, it should be loot that could kill something, otherwise it's just a waste of time, since no one will pick it up, since no one will buy is, like a 9mm Mauser for example.
5: The use does use the P90 in real life, it's also a gun that could be imported, due to good quality, and a good choice for private security, and police. same with the FN FAL. even though it wouldn't be as common.
6: There is a nigh scope version of the FN FAL, but it's not in game, so yes, scopes can be mounted to it. if that's what some of you are suggesting.
-Ulrek-