There is on another forum a user who started a small B&W photography shop in Paris. Since I don't live there, I have never done business with him. But he's your best bet when it comes to silver based photography (I read he's one of the last to sell film in Paris). Here are his coordinates:
Sels D'argent21 rue de la r?publique
Romainville
93230
Phone: 0178457276 / 0628320666
open Thu-Fri-Sat 10am-1pm and 3pm-7pm
Bus 105, 129, 318, 322 exit at Carnot