My AD was a GP dealer many, many years ago
Somehow he never sold this one and kept it for ever in stock. Don't know if he wanted to keep it himself or not but I knew he had it. About 2 or 3 years ago he showed me this piece.
I see him pretty often because he is my Zenith / Panerai / JLC and Patek dealer
But I believe he stopped working with GP 10 years ago
Anyway, yesterday I sent him an sms and asked if he still had the Marine Chronometre ... I told him it would look much better on my table than in his attic or basement 
Not knowing he used it or not or if he even still had it
He replied that he still had it and it would indeed be better on my table 
So in fact I bought a NOS (new old stock)
He's not just any AD but I would consider him as a friend, I'm glad he offered me this piece.