Are there really no canonical Gifted Merceres? By that I mean none that are mentioned as individuals with a write up as part of a covenant since obviously they exist.
I realize that statting up even one would constitute something like 8% of the Gifted Mercers in the order but it stands to reason someone would have written one up.
Not to my knowledge.
Which is why I designed one for the "More Magi of Hermes" project aka Anulens Connectens some 3 years back. That's perhaps the closest.
Considering there are 12 in the order and every game has 3 people wanting to play one... stating up even one in canon could be problematic.
Except we all have to have Parens since it is a True Lineage.
Ghost found one in GOTF. Xavier is a Gifted Mercer who is a resident of Durenmar. He doesn't have a full write up, he is just a line in the "Other Magi" section on page 61.
Ophilio of Mercere is a member of Aedes Mercuriii, a retired High Priest of Mercury and a longevity specialist mentioned in F&F, page 85.
Accursius Adiran and Volante Adiran are both Gifted Mercere members of the Oppida of Histria and mentioned in AtD, pages 76 & 77.
I statted up Ophilio for Legends of Hermes but the Belin chapter was cut before publication. It was included in Sub Rosa #8 if you want more information!
Provencal also has Guillermo of Mercere, a rather brash member of the Cult of Heroes and certamen champion (F&F pg 112). Again, no stats - I think the only statted Mercere magus is the template in the corebook.
Are they really that popular?
In all my years I've never had anyone want to play one. One saga we decided to make a covenant with only representatives from 2 Houses, in an attempt to make House plots more useful by activating several magi. we let the saga's novice choose the two houses, with only a cursory knowledge of them. He chose Mercere and Merinita, and two of us designed a pair of Mercere twins sent to Loch Leglean tribunal to take control of the Redcap network and "civilize" the area.
And in all my years of sagas before/without Trinunal books we had but a single Gifted magus Mercere defined as ncp.
There's nothing like scarcity to increase interest. I don't know if they're all that popular, but some people see a small restricted group as somehow exclusive and even elite.