I think that you reply may have been a bit hasty. Didn't the later cars have the remote lever for the flap release, thus not requiring a lockable filler cap ? If so, then I doubt that one will be available from Ford.

If this is the case, then I do know, from past experience, that if you want to fit an earlier locking filler cap, then one way to do it is to drop the fuel tank, and change the filler neck for one off an earlier car (direct swap for the later ones, but has a different aperture where the caps fits in) and then buy a cap from Ford, if still available.