Most of the Buchons carried more than one number, in Red and Yellow. These were 'Fablon' self-adhesive numbers, changed as required, in order to give the appearance of even more than the 27 aircraft obtained for the movie. Some even had one number on one side, and a different number on the other. There were, I believe, at least three 'Red 13s' at any one time !
There was a recent article in a British aviation magazine (Aeroplane, I think), covering the discovery of a great hoard of 'stills' taken during the production. Perhaps the author can help, or put you in touch with the owner/photographer. I'll find some details and post them here.
One thing which might help; as a general guide, those Buchons with a three-blade prop were normally used for ground-running and taxying scenes, and those with the four-blade prop for air to air scenes.
Any Buchon extant today, particularly outside of Spain, is virtually guaranteed to have appeared in the movie; had it not been for Hamish Mahadie buying and/or leasing these aircraft, they would have been scrapped around the time the movie was made (1968 ).