OK, this one is not as bad as I thought. Use a tracker, it's the only way... I tried it for a bit by cleaning up the zone and it was tedious and the ghoul only spawned about 3 times in a couple hours. So I decided to try to find PHer. There is a definite PHer and the spawn timer is 40 seconds. Here is the method.
Go into the desert area north and east of wizzie spires. Put up tracking to normal and auto refresh. If the Ghoul of Takish-Hiz is not up, slay everything until it is. After it pops, give the zone a few minutes to settle down and respawn the mobs that you have killed. Then track and kill the Ghoul, and set timer. When something shows at top of track again after 40 secs, kill it again. Rinse and repeat. When you get agro from mobs, just wait until PHer has popped, so you know what it is, then kill mobs, give a bit for them to respawn, and kill PHer and watch timer again.
When I did this, here are the spawns I got and how long it took to get the anchor.
12 * Ghoul of Takish-Hiz
2 * desert madman
1 * sand scarab
2 * a zombie
1 * dry bones skeleton
1 * a dune tarantula
Good luck.