Coastal Cultists Mod
This mod greatly increases the chances of the Cultists spawning next to a coast.
Works even better if you set ‘Lake Odds’ to ‘None’.
Inspired by this thread:
https://steamcommunity.com/app/289130/discussions/0/1456202919982456383/
An alternative is to replace WorldGeneratorSettings.xml with the linked Pastebin file: