I have looked for the past forty five minutes while flying with speed boost and have yet to see a single one in the farmworld. As previously shown you cant use farmworld obelisks to get to the eldritch dimension anyway but you do need cultists to progress in the eldritch section at all. i think that there should be a crimson cultist spawn egg for sale in the market like there is for coven witches, I'm not sure if it would be at all possible to fix witchery circles not generating though.
On a related note i think there should be a crafting recipe with say 4 eldritch eyes amd five void metal blocks that allow you to craft the spawn eggs for the thaumcraft bosses.(yes they do have spawneggs they are: Spawn %s the %s, Spawn %s Eldritch Construct, Spawn Praetor %s, and Spawn Crimson portal)
It is a common misconception that the farmworld is just another overworld, which is not, the farmworld is not the overworld so structures wont spawn on it, if youre looking for structures you should look in the overworld.
There should be a crafting recipe for the Eldrich portal itself. I will verify this tonight as I will be on that pack looking into updating a couple things.
This would still require a way to get crimson cultist because all of them will be gone from the overworld
I know there was another way to get these on other servers. I will need to look into this. Might take a bit as I am pretty busy with other things. I will look into this though
From what I remember last time, you could buy thaumcraft crates from the questing shop that has a chance of giving you a cultist spawn egg I dont know if its still there
If you can make it inside a Eldritch dimention to fight the boss inside there is a small chance that the boss you fight will be one that spawns in the crimson cultists at a portal inside the maze, At this time this is the only way I can think of to get crimson cultists when their are no portals in the world to obtain them at.