Took about 3 hours of running around the south end of the zone killing everything that moved before I finally saw him. To be fair I spent the first hour just running between the spots indicated on the page for the Dark Assassin, concentrating on the listed place holders. But then I got bored and started killing everything more broadly. He finally spawned at approximately LOC -1000, -5450. It might (probably) have taken less time if I had stuck with the original plan, but whatever.
____________________________
Maulis Thefool, Ranger of the 86th season on Firiona Vie...