I don't have anything for you other than a couple of thoughts.
You might see if you can locate some period gun magazines. Shouldn't be hard to find. Guns & Ammo, Shooting Times. They will at least give you a guide on what might be period correct. They are heavy on pictures.
The current staff at those magazines might be able to steer you in some direction. They get a lot of free stuff from manufacturers. They might even have stuff.
For God's sake please make sure all the firearms are "period correct" or we'll never hear the end of it around here.
This isn't going to be some kind of anti-gun hit piece I hope.
Matthew McConaughey:
“It’s like my feeling about gun control: ‘I get it. You have the right to have guns. But look, let’s forget that right. Let’s forget the pleasure you get safely on your range, because it’s in the wrong hands in other places.'” – Matthew McConaughey quoted in Matthew McConaughey Wusses Out on Gun Rights and Redskins Name
Quote of the Day: on Redskins and Gun Control - The Truth About Guns