Rémi,
This machine is highly interesting: this is the third pic known: here are the other two ones:
https://www.flickr.com/photos/280920...7632506648573/
https://www.flickr.com/photos/280920...7632506648573/
We are looking here at a very finely mottled Bf 109 G-6/AS "Rote 5". This camouflage type was sported by II./JG 51 machines, but they sported their II. Gruppe bar in front of the tactical number. Anders Hjortsberg suggests rather 6./JG 11 as this unit was known for having original camouflage patterns as well.
This might make sense for the unit, but then comes the issue of the location: the card shown by the seller states Pau, the former Stab and I./JG 101 base close to the Western Pyrénées, a place where no fighting units were ever stationed...
As the picture you found is sold among a batch of RCAF 401 Sqn pictures in Normandy, and that the military personnel seen on all pictures do wear RAF type fatigues, there is a fair chance that this Bf 109 was actually found by 401 RCAF personal...in Normandy. This would fit well with the known bases of II./JG 11...No certitude though
Cheers
Marc