This item cannot be acquired via normal means in the game. It was supposed to be stolen from the Mines Commander in the Orzammar Commons; however, it is bugged (weapon improperly flagged as equipped) and only provides common dwarven loot when pickpocketed.
Workaround[]
pc The item can be added with a console command, see this page for instructions. For those who prefer normal loot per the game's script, use this mod.