France has different airgun law to the UK, so first off check the legal side, I'm sure you cannot do any form of pest control or hunting with air in France,
I'm not sure if you need to be in a gun club to own one, or if you can shoot (plink) at home.
Then you have the UK export law because even sub 12 are legally covered by firearms law so require a customs licence to permanently export,
I imagine French customs have their own import rules as well.
So short answer is it's a PITA & probably not worth the effort.