Supposedly you can purchase some of them from a vendor known as [i]Xur, Agent of the Nine[/i], using rare currency like [i]Strange Coins[/i], [i]Motes of Light[/i], and [i]Glass Shards[/i]. [spoiler]He sort of looks like Hunter wearing all black, with a mask, that resembles a Jawa, with glowing yellow eyes.[/spoiler] I think his shop is that black market-looking area with all the Fallen and Cabal guns located under the Hangar.