There are more guns that I found on Youtube and Google that you can make and put into the add-on section.
Franchi Spas 15: An Italian shotgun made by the Franchi Firearms Company based on the Spas 12 model.
Capacity: 6 rounds
Barrel Length: 406 mm
Pic:
http://www.world.guns.ru.shotgun/franchi_spas15.jpgJati-Matic: An automatic, open bolt, blowback submachine gun made in Finland.
Capacity: 20-40 rounds
Barrel Length: 202 mm
Pic:
http://www.imfdb.org/images/d/d3/JatimaticSMALL.JPGFN MINIMI SAW: A machine gun that was made by the Fabrique Nationale.
Capacity: 200-300 rounds
Barrel Length: 465 mm
Pic:
http://world.guns.ru/machine/fn_minimi_m249.jpgH&K G11: An assault rifle that is a prototype made by Heckler & Koch.
Capacity: 80 rounds
Barrel Length: 540 mm
Pic:
http://www.militaryfactory.com/smallarms/imgs/hkg11.jpgThat's all I have for today and you may google these guns up for more information.