The above list of ateliers was put together by T4phage. He did not explain if he had firsthand experience with them. Seraphin allegedly do not allow visitors or direct orders. They do have a retail shop...in Moscow.
A shop called Purcell on the Champs Elysees (inside a gallery on the north side) has a large selection of Seraphin.
I just keep posting the same list each time someone asks about bespoke leather jacket makers. Don't shoot the messenger, FullCan.
We called Seraphin's shop and were told no visits. Theo Fil also carries a bunch of his work. Or they did in 2001.