I went to the Legendary Forges today and noticed I can start manufacturing Legendary Armor, but do not know where to get the molds from. Does anyone know what NPC or monster has these special items?

Most, if not all, molds are dropped by FB bosses. For instance, the Hand axes of Demonic Roar mold is dropped by Quingzi of FB 29, the Wheel of Fate mold is dropped by Hercule Trioc, the FB 39 last boss. Drop rates for the molds are generally under 5%, and the futher away the party's (or killer, never understood the loot parameters), the more likely you are to get just coins. For example with my herc at 43 I was able to solo FB 39, and i did so several times, and each time i never got just coins, and alot of the times i got several three stars or molds per boss. By 47 or so though I was getting alot of coin only drops. Not to say that a lvl 70 couldn't get molds from an fb 39, but its far less likely.

some molds can be gotten from turning in many dragon orders
some molds that can be gotten from fb bosses can be gotten via mysterious chips(worry about this at 70 or 80+)
pwdatabse.com to search specific molds ect