In the very beginning of the game, in Doc Mitchells house, when you wake up look around the room the medical stuff is in. Right next to the desk (think it has a chemistry station thing on it) there is a box with a "Broken 9mm SMG".
If you have a repair skill of 35 (Pretty sure it's 35) you can repair it and take it without losing karma or anything.
If you don't have 35 repair, you can just come back when you do and take it.
It's pretty good, and it does 96 DPS at about 80% condition. Requires only 3 STR, Worth about 700 caps when it's fully repaired, and there are plenty of mods for it around the Mojave.
Hope this helped someone!