When I'm bored, waiting to get into a battleground, or just when there's nothing else to do, I just go do laps around the searing gorge. I get about 70% mithril, 10% dark iron, 10% thorium, and 10% other (iron, gold, truesilver, ect). I usually don't really go anywhere else unless I'm looking for something specific. Eastern Plaguelands is a decent place to look for thorium, look around the mountain borders, and the two scars, and you can find a good deal of thorium.