Seems like the original discussion topic has been lost to time but you get the idea. It’s been talked about to death and there’s mentions in the above ones that it is intentional that Kaisan only drops his amulet in campaign because of how flexible/powerful it is.
It’s somewhat time consuming if you get a lot of late spawns in Korvaak’s Tomb or the Astral Fields but if not, it’s not that bad. When I was farming him last, I developed this route:
Rift to the Ruins of Abyd and run east to the Temple of Ateph and check the first floor, if he’s not there rift back to the Ruins of Abyd and run west across the camps passing by the Infernal Wastes rift and head into the Tomb of Sethan. Run through to the other side, go out the other exit, then run north across the bridge into the Tomb of Nephos and run through checking again exiting out the other side.
If you haven’t found him by this point it’s an unlucky run but still not much left to check. A good chunk of my Kaisans were in the above spots so were pretty quick. Most of the quick runs I had were ~5 minutes or less. If I were using a Vanquisher character they would be even faster.
Rift to the Korvan City and run through to the Sunward Spire, head up and up and up (this is by far the worst new spawn point). Exit out, run towards the city end into the Tomb. Check both floors, stop before Kymon. Rift to the Eldritch Gate and check around the middle of the area. That’s all of them.