I can confirm that they drop just fine in acrylia caverns. Got them off both grimlings and bugs. Not sure on skellies but I dont doubt it. Also starting a stack of simple binding powder as well.
Also drops off of "Greenfoot wizard" and "a Broodlands worshipper" in The Broodlands. This is a decent farm spot but I keep hoping I'll find a farming spot that drops a whole lot more!
Best place I have found for this is the caster Grimlings in the outer part of Acrylia Caverns...even the skellies prior to the lava room often drop this powder.
I more or less farmed everything from the named Alchemist (who repops quickly), through the jail, and up the next level elevator to the Queen's level. I did not clear the Queen's room, just the council room. Don't forget also the spellcasters just before the elevator.
I found it drops off the following mobs, some of which have been mentioned here:
a honeyblaster a council notekeeper a council historian an arcane researcher a bixie poisonbrewer a cultivator drone a warpriestess a harverster drone
I may have gotten 6-9 an hour with a 68 Monk, could clear everything I mentioned with a few minutes to spare before repops. Save also the Bixie Meat, decent sell rate (11pp per) and stacks in 20. (Not the bixie parts though, those are good for baking but not much else.)
Not sure if this is better than Dulak or not, the mobs certainly die faster but the rate seems a little less.
Also drops from Bixie Spellcrafter. There's a certain wing of the Hive that has lots of these and Arcane Researchers. Close to that area is the area with the Bixie Poisoncrafters and Cultivator Drones. Farming these rooms seems to yield a good amount of powders.
Drops on Broken Skull Mystic, Broken Skull Seer, Broken Skull Augur, Luggald Subvertor, Luggald Zealot, Luggald Concealor, and Luggald Alcolyte. Not to mention the various names. I spent 2 hours in this zone and got over 60 of these to drop.