Used pizza ovens and other pizza-making equipment can be found on sites like Pete's New and Used Restaurant Equipment and Bake Deco and in online auction sites like eBay. These stores allow restaurateurs and enthusiastic amateurs to purchase the equipment they need to pursue their craft at a reasonable price.
Pete's New and Used Equipment gives buyers access to used and refurbished pizza ovens and other restaurant equipment. Ovens are guaranteed to work, but may have seen varying degrees of wear and tear, though most often they are for resale due to the acquisition of newer and more efficient equipment.
Bake Deco's website has a large catalog of used pizza ovens. Ovens of various sizes and capabilities are available depending on resale conditions in the market at large. These ovens are cleaned and refurbished before being offered for sale, meaning they can be put to work immediately after purchase and delivery.
Auction sites like eBay give buyers a chance to bid on used pizza ovens in various conditions and from various sellers. These ovens have various shipping policies depending on the seller and can sometimes be had by direct purchase for a certain price, although more often they are available strictly via the auction process hosted by the site.