I recently did my cudgel quest and wanted to post some updated info regarding this guy since everyone I talked to was also confused on his spawn points.
As of September 2022 on the Yelinak server, this mob does spawn in the sewers in East Cabilis however he has placeholders! There are a few spots he can spawn, but I found that it is easier to get him to spawn in the three "rooms" that allow you to fall into the water. Each room has 2 mobs (some cycles have a single mob) that will circle the room. These are the PHs. Simply kill them in each room and the outcast will eventually spawn.
You may be asking, how do I get to each room since the walls close? --Good question! What I did is go to the middle room, then park your highest level pet just outside the room. If you drop into the water, you can swim to each room via the sewer then you can simply command your pet kill each of the room's PHs. The pet can go between the walls :) (use your camera to change the angle of the view and you can get a perfect shot of the mobs)
This method will allow you to spawn him quicker, but you do have to be fairly active. You can use the single spawn point others mentioned if you are more AFK, but that is much slower.