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.
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Ummmm so that could also apply to the coins you earned to buy it. Oh wait that's to much logic I better stop before I hurt myself.