Priest of Derketo can be found in the Jungle, particularly at the Pagoda of Endless Lust. To capture a priest, high priest or Archpriest you will have to clear the camp to the left (as you look at the pagoda) and the further left camps (2 camps). From cycling those you will find priests (t1, t2, t3). I have yet to ever see a named one, but you just keep clearing those and you will get what you need. Also by setting up a thralling location at the highest point of that ledge, you can farm the area for thralls (named: cook, armor, blacksmith, carpenter, entertainer, taskmaster, archer and fighter). This has been there since July when I started playing.