Once you purchase the Gun Runners Arsenal DLC these weapons will be sold by characters across the Wasteland. You will be able to find them at just about any vendor who sells weapons and each has their own special selection of unique weaponry. 10,000 points of damage can easily be accumulated if you stick with your unique weapons only and do quests or random location cleaning. The full list of unique weapons can be found HERE. Just for clarification, unique weapons must be named weapons that are different from their regular counter parts like Paciencia---Hunting Rifle or Maria---9mm Pistol.