Quoted directly from the Trade Skill Sticky at the top of this page:
Locke, Troll who wrote the Trade Skill Sticky wrote:
Q. How do I specialize my weaponsmithing?
A. First, be above level 51. Second, go to Everlook, in Winterspring. Third, look for the three people hanging out... I believe in the bank... You'll notice them easily; one is Lilith the Lithe, a dancing undead. Another is a human (I believe his last name is Scourgebane... funny, as he is watching an undead dance, hehe), and the last is a troll. These three are the masters of the weapons; their quests will get you into the path you desire. You can ONLY be one type of master. You will receive 4 recipes from them (or on the quests; I know the swordsmith will pick up the plans for Corruption, and the hammersmith gets the plans for Serenity). You are now a weaponsmith master.