You can continue looking for used rowing machines for sale. Usually, you will set notifications to stream in when sellers list products in your preferred Marketplaces. You will then get notifications for new listings for used Concept2 rowing machines.
But for Marketplaces that don’t allow you to set notifications, you can check back often. Also, you want to do this if you don’t find used Concept2 rowers. So, consider visiting the Marketplace often if there are no used rowing machines for sale.