I wholeheartedly support this idea.
Here are some ideas, which if I had any skill in coding or modeling I would have attempted long ago:
Winchester rifle: Medium damage rifle, holds 8 rounds, very accurate.
Sharps rifle: Very high damage, very accurate, only 1 shot with a slow reload.
Single barrel shotgun: A breech-loading shotgun, like the DB shotgun but with a longer barrel and smaller spread.
Colt Peacemaker: A standard six-shooter. It's a single-action revolver so it should have a slower fire rate than the current revolver add-ons.
Oh, and maybe a Colt Navy Revolver.