He spawns from any of the Nightmarish Guards in this area around the Grounds ZL.. Look through the false picture frames, end of each hallway. There are a total of 4 PH's, he can spawn from any of them. Split them with a few minutes in between, sometimes you get lucky and have back-to-back spawns. The bow is his hot item if your selling or plat, and of course, who could resist a scuffed bag.
I've looted like 2 in my eq history, I have horrible odds.