There is a dwarven weaponsmith in the Dwarven District of Stormwind who can craft with lightforge iron. His name is Grimand Elmore.
I've packed the iron you found into a crate. Take it to Grimand and tell him your tale. I'm sure he'll oblige someone on a quest such as yours, and craft for you a weapon - a weapon to give even Morbent Fel worry!
That is quite a tale you have. And lightforge iron! Not for years have I worked with such a metal. It will be an honor to craft with it again. And you must return to me later with the story of your battle against the Necromancer.
But we get ahead of ourselves. First, your weapon against Morbent Fel...