We got this guy after much misinformation, just last night. As you zone out of Katta Castellum into Tenenbrous Mountains, look to the left. Follow the zone wall until you reach the first Coterie outpost. This is where he spawns. It took us 3 hours of straight killing every pop at that outpost, but he spawned. If you are going to try kiting, it is safe to kite along the wall, but be aware - the Coterie have a LOT of Hps. You may not kill the entire camp solo before respawns. Bring a group if you can.
Good luck all and CHEERS!