The Gun Runners store on the east side of New Vegas has a locked fence and several guard blocking the entrance to the "factory." Pick the lock and the Gun Runners will begin firing at you. Kill them and loot their bodies for Combat Armor, Hunting Rifles and Combat Helmets. All of these items are worth money, and each Gun runner has about 1,500-2,000 Caps worth of loot on their person. Enter the building to find more Runners to slay. After doing this, approach the Vend-Tron robot at the Gun Runner shop, who has 8,000 Caps to burn, and sell it your loot. Now, travel far away, wait for three in-game days and return to the area to find the Gun Runners have respawned and are ripe for the "harvest."