Keltoi Fogou,
In the "ant room" and Dai cavern area.
Is very rare. Although was fortunate to log in for my second item hunt of the day, and got it off the first Keltoi Spiritualist I killed.
Keltoi Spiritualists dropped this, the scout bracer (name? +2 Longbow, etc.), Insurgents Vest, Wanderer's belt and a few others. Dai cavern is very good place to hunt items in Keltoi, although sometimes you get nothing for ages.