You firsat have to have the TwoGuns mod which makes add-ons possible.
Gte it
here.
Then read the readme inside of it and do what it says, finally, place the addon zipfiles into TwoGunsFolder/tgm/server/mods
Be sure to download the spas on the same website of the TwoGuns Mod.
Also, i dislike the flamethrower without the ability to set people on fire. D:
Spawn the weapon by entering the world editor or by typing this into the console:
weaponnameatplayer();
For the spas that is, spas12atplayer();
Flamethrower is, flamethroweratplayer();
Minigun is, Minigunatplayer();
Sniperrifle is, sniperrifleatplayer();