Sorry for the long wait. Got busy over the weekend.
He spawns when you hit one of the 5 Traitor's Gravestones marked on this page:
https://bdocodex.com/us/npc/20805/
So I'd recommend using those as the locations for this mob.

Ah, sorry.
I think it dropped from this mob actually:
https://bdocodex.com/us/npc/20811/

Oh, I didn't realize I had the ability to submit edits to the pages directly myself, I have now done so.

Not sure if this is the right place to put this, but I didn't see a better one. I just got a drop of Kehelle's Artifact - Max Stamina at the Marie Cave node. I think it only has a chance to drop from the big mobs (Green Orc Skeleton Warrior) that spawn from hitting the traitor's gravestones there, n...

The Nouver subweapon AP values display "NaN" when viewing them at Tri-Pen levels.
Link: Example Nouver Subweapon
This has occurred on multiple subweapons I've checked, not just this linked one.