Bievres used camera fair happens every first week of June (this year it was postponed to the second week because of the European elections). Bievres is located south west of Paris near Versailles. All kind of photographic equipment can be found at this fair: cameras, darkroom equipments, films, studio gears, pictures and books, other gadgets and even watches. Of course Leica is very well represented. All kinds of accessories could be found and people are coming from all over the world (see flickr photo description for more details):
Here is another link with more info on this event. Bievres has also a great photographic museum.
Thanks to Xavier Lhospice for the report & pictures.