It’s not easy to get a T3 or T4 priest for Derketo. Regular priests and High Priests spawn quite regularly though. At Pagoda I’d Boindless Lusts just keep farming through all the camps and the Pagoda itself and one (T3 or4) will eventually pop up. It’s all you can do other than win the RNG lottery to get a very specific purge and then another lottery during that purge to have a high tiered priest spawn. You’ll have better luck to just keep running the Lemurian camps and the Pagoda.