Well...?

[POSSIBLE SPOILERS]











A light machine gun can be found near the back of Quarry Junction inside the Deathclaw Matriarch's cave.
Can sometimes be found on Super Mutants at Black Mountain.
At higher levels the light machine gun can be purchased from gun runners outside of Freeside.
Can be purchased from the Brotherhood of Steel at Hidden Valley, when the Elder McNamara allows you to buy from their armory.
LMGs can sometimes be found on the bodies of NCR soldiers wearing Salvaged Power Armor in the Hoover Dam.
Sometimes at Jack Rabbit Springs equipped by Super Mutant Masters.

Easiest one I think can be acquired at Quarry Junction if you explot the Deathclaw's inept AI. Specifically, if you sneak your way ontop of a large truck/rock outcrop/bucket/etc, they don't realize they can hit you and are thus free pickings. You have to get up there while hidden, though. If they're tracking you they will figure it out. Get yourself into position, snipe away, and it's at the back of the quarry in the nest.

Black Mountain. Several of the mutants have them. They are in really terrible condition though.

i find the 12.7mm submachine gun to be better than the light machine gun its in the bloodborne cave north of gypsum quarry and has nightstalkers in it, the gun is behind a locked gate(the key is by a campfire further in), there is a tripwire just inside the gate, be carefull of the gypsum quarry on your way there tho its full of deathclaws, the 12.7mm sub machine gun does about double the damage and has about 50% more dps of the light machine gun, it just has a small clip, it can be silenced too. you can also buy one from the brotherhood but only afetr your a member

Where do you get 12.7mm ammo?

After killing a whole slew of Super Muties over on Black Mountain I was able to get mine so I would suggest looking there, I was able to obtain my Light Machine Gun there with no problems. (Also the weapon mod that increases its magazine size from 90 to 200 rounds is godly.) :tops: