"M79 grenade launchers are destructive devices, meaning you will need a $200 tax stamp and a months long approval and background check process to obtain one. However, as long as it is legal in your state, you can get them.
They’re not exactly easy to find. Not a whole lot were produced for the civilian market. I was only able to find one for sale, here at AUTOWEAPONS.COM
From what I can tell they typically cost about $5,000–10,000.
Explosive rounds are hard to come by and each individual one must be registered with an additional $200 stamp and background check. You can use buckshot/flechette/beehive rounds as well as smoke, flare, and chalk rounds without restriction, however.
A better option would be a 37mm replica. 37mm launchers are designed to shoot flares and thus aren’t considered weapons, and can be bought freely. The 37mm M79 replica, the TBL-37 (TBL-37 Top Break 37mm Flare Launcher Wood Stock) is kind of ugly and certainly not an exact replica, but it has much less regulation and is probably a lot cheaper, if you can find one. You can only legally shoot non-weapon rounds from it, though, such as flares or smoke. You can’t use any lethal rounds like buckshot or even nonlethal rounds like beanbags."
