I found him up in the Northwest spawn.
Take out the stoneshell pest that wanders into the chamber. I sent in pet alone whilst I stayed invis in outer chamber, nothing assisted the pest.
I then nipped around the corner to stand on top of the raider spawn opposite Garath. Engaged the raider, the other raider standing beside Garath assisted but he was too lazy to join in.
Then took him on solo. Easy kill with self-buffed 110 Air pet.