Got this spell quite easily from tracer antlions (the easiest antlions) in Attohwa Chasm at lvl 44. 1/3. Only hard part is finding them. They are on the east side of the chasm. To get to them:
Just keep going straight once you get in Attohwa Chasm. Once you get to the chasm, cross it, and go straight again. Simple enough, but no one makes this very clear where they're at.
Oh, and MAKE SURE you bring antidotes. They're cheap enough from vendors, and they can save your butt if you're not /whm. The antlions use a very nasty poison move, venom spit, that goes through shadows. It does about 12 hp per tic. So best to bring some antidotes.