The Order of Juno. From South of the Sun (AG 3040). For Realm of Power : Magic or Ancient Magic. I like the method of acquiring spells. But how translete this in the rules (AM5) and can we use the sames rules for Realm of Power : The Infernal ? Because Demons pretend to be Gods and can use the same artifice... You can perceive the possibilities...
The Priestesses of Juno have not yet been updated to 5th edition and I suspect that if they ever are, their method of obtaining and casting spells would be streamlined to better fit the 5th-edition aesthetic.
The 4th edition rules could probably be used with a bit of tweaking...
The Hyperborean Hymnists from Ancient Magic are vaguely similar in concept, if not in execution. Perhaps you could adapt those rules?