Within the expat community, there is usually a reasonable market for used appliances and furniture with the summer influx of new expats each year. If you are in contact with any expat groups in your area, you might ask them about advertising in May or June in their bulletin.

The trick is that many associations (and most of France, for that matter) pretty much shut down during the months of July and August. The towns that have brocantes (boot sales) usually run them in September and October, which doesn't do you any good.

Otherwise, check the pages jaunes (in print or online) for "Dépôts-vente: meubles, équipements pour la maison" and/or "Matériel d'occasion pour particuliers (achats, revente)." The other option is eBay.
Cheers,
Bev