I got this one yesterday. I'm going around trying to fill in the gaps in my spellbook by going after the dropped/quested/crafted spells. I was splitting my time between doing this and trying to get the spell drop in ToFS so I didn't get too bored grinding in the same place for long periods. Finally got both and am very happy although I am sure both will be obsolete soon.
BTW, I tried doing this in Dulaks for a while but the path to the ships was a bit too dangerous so I settled on the fort even though the troll plunderer/marauder spawns are somewhat harder to find than the trolls aboard the ships. You have to kill many pirates of other races to get the trolls in the huts around the fort to spawn and it has to be the marauders/plunderers. The Broken Skull mystics and warriors don't drop the piece you need from what I have seen.