If you look under "Haute Savoie" there is a complete list of Vide Greniers under this site which are all around the lake district on the soutern side.
http://vide-greniers.org/
There is a huge and extremely good VG on 1 May each year at Allinges where one can [and we do!] pick up amazing bargains, especially CDs in good condition for 1€, as well as childrens' toys.
On the last Sunday in August, there is an equally huge VD in the centre of Evian here which is also very good. Additionally, there are several others in Evian which take place at the Parc Dolfus throughout the summer, and also in Thonon on a regular basis - one simply has to consult the schedule.
Hugely enjoyable, even if only for a morning out.
Who knows, we might even find a piece of Lalique glass worth a fortune one day [dream on].........