You can find copper pots in department stores, second-hand shops and brocantes. But for brand new copper cookware, your first stop should be E. Dehillerin. A famous family-owned Paris cookware shop that has been around since 1820, E. Dehillerin is hardly a secret. But if you've never been, it's worth a trip for copper pots and other quality cooking equipment, or just a window shop. And if you're not planning to be in Paris anytime soon, you can order online via their website.
Other cookware resources in Paris: A. Simon Mora La Bovida (36 rue Montmartre, 1st arrondissement) - Kristin Hohenadel blogging from rue Vieille du Temple, Paris, France. She can be reached at kristinh @ apartmenttherapy . com