"Sunman", thank you so much for the info. Things are much more clear to me now.
I live in France, I've been lucky enough to buy a Classic Roadster Cobra and to find the Certificate Of Origin in the trunk.
Now I'd like to buy another one. I found a Cobra and a Sebring, but without a certificate of origin, the custom will charge me as for a normal car which means 10% custom fee + 20% VAT. And in a second time I won't be able to get it registered.
Is there any way to get in touch with Ryan Martens ? He may have access to some archive and he could even sell copies of Certificates of Origin ?