according to wow head there some npcs have a lot higher chance of dropping them, once I get to that area i'll make a profile. Ik'thik Fear-Shaper - NPC - World of Warcraft only 2 out of 3 dropped. 67% chance to drop, the real figure will be lower, but i'll kill quite a few and see what it changes too.
The real figure will be the same as all the other ones. I would use a low level grind profile, perhaps jade serpent to kill as quickly as possible.
I can 100% surly say that if you got decent heroic gear you can farm the level 90 mobs for better yeld than the low level mobs, as you run out of low level mobs to kill, and the high levels have higher drops testet and confirmed..
This is a profile I made using one of Kick's farming templates. I made it to farm my Black Prince Rep. Farms Mogu in Vale of Eternal Blossoms. Use with Questing bot. Alliance vendors/mailbox.
Fishing pools is doing the job for me. They come in the sealed crates. Not guaranteed but I have gotten quite a few.
http://www.thebuddyforum.com/honorb.../72207-howling-wind-cavern-motes-harmony.html Lots of weak mobs, i've gotten about 8 motes in half an hour. Might be my luck.