I had Metalsmith on artisan or so when I picked my first profession, and I did do the quest regarding the Superior Forge. I ended up switching my profession and decided to switch back to armourer a few days ago. I've maxed out apprentice and journeyman, also have got expert tier proficiency maxed. The quest dealing with the Superior Forge doesnt appear and i've checked NPC's in Bree, Celondim, and Thorin's Hall. Any help is appreciated.
Perhaps since you have already done the quest, you can't repeat it. I take it its not letting you advance to the next level, even though you have enough exp to do so? If so, make sure you are talking to a Metalsmith, not a supplier, weaponsmith, ect, specifically a Metalsmith.
it sounds to me like you need to complete the superior forge use quest again. when you changed profession you lose all progress on any of the 3 crafts that aren't shared with the new craft and i would think you would lose the superior forge skill. you can check if you still have it in your character passive skills list or standing near a superior forge and look for the forge/superior forge icons on your character bar. if you cant find any npc in thorins hall with the quest then /bug it :P