Kim, my 4th Gt grandfather was a French pow and was sent to the parole town of Selkirk in Scotland because he was an officer. I made a breakthrough by going to RAOGK (Random Acts Of Genealogical Kindness) and contacting some of the volunteers in France. I got his military record from
SERVICE HISTORIQUE DE LA DEFENSE
CHATEAU DE VINCENNES
AVENUE DE PARIS
94306 VINCENNES CEDEX

Give them as much info as possible.
That's all I can think of, but don't give up, it took me 12 yrs to break my wall down. Happy hunting, Norm.