Plenty of them in Geneva.
Go to the Acacias where many big garages are together, they have many used cars for sale.
Or head to Lignon, on your way you'll find the ROC and near to it many other used car lots ( ROC SA Route du Bois-des-Frères 85 1219 Le Lignon )
Finally at Meyrin near to the train station you'll find many more used car lots. You can also find what you search for just in front of Conforama in Meyrin.
Or simply look for it at
www.car4u.ch and
www.auto24.ch you'll find a broad selection of used and new cars near to you.