Have you tried Googling their names to see if any info shows up? In the U.S., there is a site called anywho.com that gives info from U.S. directories; there might be such a site in Europe. You could see if British libraries have phone directories from the 1950s archived but that would only give you their addresses back then, not now. In any case, I would try going to the largest library near where you live in France and speaking to the reference librarian there if Google turns up no leads.