The Instruments of the First Will is a cult of Juno worshippers. They believe that we should go back to the way things were when the First Civilization was around, which is that we humans should subjugate ourselves to the Precursor race. I imagine it would be a bit like living in Arkansas.
As we've just seen some Juno-themed cultists in World War I, it's likely that there have been Juno worshippers since the fall of the First Civilization. However, I don't know that they were the same as the group that currently operates today.
It's not often you'll hear me use the phrase "I don't know," by the way, so do make sure you enjoy that.
Anyway, there is sometimes, but not always, a Sage involved. Honestly, with Juno's digital consciousness out there, there could be groups of them anywhere. There was a group of them found in Abstergo Entertainment Montreal, and I suspect there were some mucking about in Paris last year, around the same time we were.
I've seen intelligence that suggests that the Instruments and Abstergo have an uneasy working relationship, helping each other locate Precursor artifacts. I don't fancy the idea of either group getting their hands on too many. At least Abstergo is the devil we know.