How to get Thorn?

Is there a way to obtain the Thorn in year two of Destiny? I don't know of any way to get it.

I'm looking for it because Thorn is my favorite hand cannon EVER.

For starters - there is no year 2 version of Thorn.

With the removal of exotic bounties, there are no ways to specifically target Thorn. However, you can run year 1 content (raids like Vault of Glass or Crota's End, or the Prison of Elders) all of which have a chance to reward Year 1 exotics. Finally, Xur sometimes sells legacy exotic engrams for 36 strange coins. These will always decrypt to a year 1 exotic, with a strong bias (but not a guarantee) towards ones not already in your collection.

You can get the Thorn from nightfalls, raid drops, three of coins or if you have year 1 version you can just buy it from the kiosk

Now that Year 3 and Rise of Iron have come around, it's time for an updated answer. There is a new version of Thorn, and the quest for it is given in the same way as in Year 1 - there's a small chance to get the quest upon turning in any bounty.