In Grimling Forest, the camp directly outside the entrance of the caves to the zone-in to Acrylia Caverns, and the caves themselves are the place to be for Windstones. Clearing this I at least get 2-5 windstones, and the respawn is fast. I also use this place to farm some steel ingots. I usually get 1-2 per clearing. Level 85 BL.
I have been doing the Grimling camp raids across the zone and these grimlings drop them far less or not at all. I also hunted for windstones in Twilight Sea, but the killing is slow there (too few aliens that drop them, and they do not drop from Elementals). Twilight Sea is still good for the Essence of Wind though, they drop exclusively from the Air elementals (surprise?).
Edited, Oct 30th 2013 4:25am by Treesong