/setwaypoint 8530 8930
He's tucked away in a corner. If you're coming into Arkella Estate from the west or south side, you'll see the mobs for Carnage : Battus et brouillés just south of the big ramp you'll climb to reach his location. To get to him, take a left just before the sourcewell there, used for Assaut : Domaine d'Arkella. The Rusted Band for J'aimais pas leur musique, de toute façon can also be found there.
If you're entering the estate from the east, go up either of the ramps around 8690 9040 (location of Des survivants savoureux), then head northwest to get to the ramp that leads up to the sourcewell. Turn right, then right again at the Lifespring, down the other ramp and through the other mutants until you see him.