Try the Fly Trap in Misty Mire on Tortuga - that's where I got mine, took 3 tries.
Once you get in the Mire, walk to the left and you'll see 3 torch-like things. Stand in front of those and pick of the fly trap there. The level varies but is often a fairly low trap. If you get to the higher level undead guys, you went too far forward.
Good luck
