Wizard City - try the Caves Krok - try Palace of Fire and Tomb of Storms Marleybone - Ironworks is where I always find it Mooshu - Cave of Solitude Dragonspyre - Atheneum, Tower Archives, Plaza of Conquest, Dragonspyre Academy, and many other locations
I have the same quest, only for Death school. I hang out in the Cave of Solitude for my ore. What I do is harvest every piece I can find in there, then I change realms and do it all over again. I pick up a ton of ore doing this. I also have the transmute recipes for Diamond and Black Lotus, because it's easier to find cat tails and ore (to make the lotus) than it is to find the actual Lotus, in my opinion.