While I was sitting on the toilet reading the weapons booklet that comes with the limited edition of Destiny I came across something xurners won't be pleased about... on page 44 it states Gjallarhorn will not be given out. It must be "earned".
haha
Edit*
I understand Xur has sold it, but if you had enough strange coins week 2 you "earned" it.
-
Not sure if this happened week 1 or 2, but early on Xur let you buy a strange coin with motes of light. I think Xur only let you buy one but you could still make a new character and buy another. The players abused this so bungie took it off his sell list, the same day. So some of the player that bought it week 2 did have an advantage.