Hi Sofia,
This company does Spanish registrations, I think mostly for British people who can’t speak Spanish well enough to do it themselves, but want to keep a boat in the Mediterranean.
https://www.register-yacht-spain.com/
They say they need a certificate of measurement instead of a CE certificate for boats built before 1998.
Somebody will have a certificate of measurement. I’m next on board in Monday, and I’ll see if I have one. If I do, I can get you a notarised copy without much trouble.
You might also talk to this company to see if they can help you. For a prospective client they’ll at least be able to tell you if it can be done and what it would cost.
Best wishes,
Andy