Mine dropped from killing Randal the vandal. He spawned in the loot cave on Uranus. Needless to say I hammered him into the dust.

I violated the [url=/en/View/bungie/conduct]Code of Conduct[/url] and was met with Ninja Justice.

Mine dropped when I killed Xylar

Other, I earned it the hard legit way... First you create a new character, must be Defender titan before you kill anything, for the remainder of the game you may never sprint. Only use Melee to kill enemies in the starting mission and DO NOT DIE, you will then collect stuff at the tower and ready to go defeat the one guy... When you spawn into the cosmodrome DO NOT and I repeat DO NOT look in the eyes of any enemy, I recommend facing down and walking that way, remember not to sprint... Ignore the mission and find your way to the skywatch, when entering the area you may look up. Head over to the helicopters where you will find a blue looking chest, open it and accept plus put on the Titan mark you will receive. Now for the fun part, head back to orbit and start the mission again only this time do the mission, grenade kills only, if you shoot or Melee this will ruin all chances of thorn... After you kill the boss you will now need to complete all missions you can in the cosmodrome before going back to the tower, no specific ways to kill in these just DO NOT swap weapons or armor in this time... Head back to the tower and grab bounties from postman or whatever and destroy the bounties immediately... Like within 10 seconds of receiving them, I suggest doing one at a time to be safe, when the last one is delete proceed to grab a fire team of level 34 warlocks with self Rez, black hammers, and gjallys... Head into the strike on earth and make it to the point where you kill the walker, as soon as the walker drops... Shut off your Xbox or ps4... Wait 5 hours and turn it back on... When starting up destiny choose your Titan again.. This will surprise you at first but you will spawn at the walker part of the strike, the warlocks will have completed the strike and will have left by now... Continue to the end of strike and grab the golden chest... Crap right I forgot make sure this is the FIRST golden chest you pick up if you got the ones previously please restart everything ... The chest will contain not only some low level bs but also a bounty lead... Take it to Xur... Xur will give you an exotic bounty called "Have a wonderful weekend" and this is exactly what you must do... Go outside and have a great weekend... Come Monday log back in and talk to ikora to finish the bounty and you will now need to complete the whole story mode with solar damage kills only, after you beat the black garden proceed to finish Normal and HM VoG and Crota, if you get an exotic weapon you MUST dismantle it before leaving the raid. Return to the speaker and but a Titan class item from him, put it on and head to crucible... Rumble... You now need to play rumble until you get 5 wins in a row without a shotgun... When you finish the 5 wins you will receive "barrel of thorn" congrats you have half the gun... Repeat the whole process with a hunter (blade dancer) and NEVER use super to receive the other half of gun... Put both halves on your warlock and accept the new mission that Xur will offer you... It's real easy just long and annoying... And congrats! You will have thorn... Good luck guardians

Legend has it that if you dismantle you x2 Gjallarhorn before opening the exotic chest in VoG, you are garunteed Thorn upon opening the chest ;)