Vide-greniers aren't exactly a location. Rather, they're a series of locations, and you can find them in most of France. Typically, a village centre closes down for one day a year for a sort of giant car boot sale/ street market/ fair, and the photographic opportunities are wonderful. Here's the most recent piece on my site about them, mixing reportage and street photography and still lifes and more. There's more background to vide-greniers here. Cheers, R.