The question is not whether or not Thunderbirds were ever sold in Europe. Obviously if Christian had one, then they must have been sold there. Nobody is questioning that.
The question is whether the Ford Motor Company ever made a 1991 SC 5 liter, regardless of which country it was sold in. And according to that site, no such car was ever made by Ford. Once again, I don't claim to vouch for the site's accuracy, I just posted the link as an FYI. The general consensus here seems to be that Ford did not produce a '91 SC 5 liter, and so far nobody has offered any proof that they did. The fact that Christian bought one does not prove that it was a factory-made car. It might have been an aftermarket conversion.