Hi there concordino,
I'm afraid you won't find any FAA certified Flight School in Spain. All training organisations (FTO's) are design in accordance with the JAA regulations, since Spain is a JAA contracting state (one of the first ones).
I know you can undergo both, FAA and JAA training back in the U.S., but you know, they are decades ahead of us in terms of pilot training.
I wish we were ruled by the FAA.
Good luck with your search.
Cheers!
