For me, they dropped in The Great Divide, where there are caves with miners in them. I think if i remember correctly, it's the mines in the north-west of zone. It's a rare drop off them though but i got it in 5 mins there whileas the bloodtusk heart took me 2 weeks of 8 hrs camping
Yes, I literally wanted to skull fuck myself while camping the miners. I was mostly killing the thurgadin miners which don't actually drop the ore. I was up to something like 30 hours in Thurg and probably another few in GD before I finally got it.