They usually stock up with several extra sets when they select a current model and keep them at home as opposed to relying on a OEM to provide past models. Even the pros will shop for used at some point if they have a old favorite that is not in stock. It is possible to run across old stock at retail stores for a while until they sell out but that's usually only one past generation model, not much older models. Sometimes you can find those in mint conditions at a used retailer like 2ndswing.com but not a guarantee to happen. There was a story going around a few years ago about Paul Casey (pretty sure it was him) trying to get Tiger to give up one of his back up sets of swoosh irons after they went out of business. Point being, over time you have to move on if you don't have pre-purchased back ups.