https://forum.atlas-games.com/t/1221-2-march-of-the-primi/6339/110
I'd asked you to name and sketch him out a bit. I don't have anything on him. I can do that, if you're not interested.
Also, Viscaria has or has read a book by another Magical Mercere, when I did a quick search.
I'm going to say that Korvin is the only Magical Mercere in Normandy, because of the concentration in Iberia. There's an Attravere in Stonehenge, too.