I wrote a weird Faerie Mystery cult for the post-a-day writing thing in November 2019: The Cult of Isis.
Fair warning: uses new rules and virtues and has never been playtested. Use with caution.
The neo-mercurians have featured heavily in some games I've been involved in. While they are a single cult as described in TMRE we generally had a few sub-cults with their own extra mysteries that was a nice way to incorporate small virtues that you couldn't write a whole cult around. I think one was focused on potent magic, one focused more on divination and had some astrological magic, and one had access to magic realm magic and was trying to find "Mercury" in the magic realm (with no success).
We also had a cult called the "Daughters of Airitech" based around the Wolf's Court from Mythic Locations. Essentially the she-wolf of vengeance was a tutelary spirit for this cult which was based at Rathcroghan in Hibernia. The cult only permitted women as members and got access to skinchanging (into a wolf), then some minor magical powers that allowed them to tell truth from lies and sense guilt. They were hedge wizards but you could extend it a bit to make it into a hermetic mystery cult.