Tough to find used. I have done a lot of research in biminis. You have a few options. Buy the OEM at your local dealer and pay like $700. Buy a universal fit one off some place like ebay for under 200. Or you could find a local boat shop and have one custom made but that could also be expensive. The best option which is what I chose, is to buy the OEM bimini from JM Camper. You can find them online. They are one of the largest Sea Doo Dealers and are located in Maine. There price is the cheapest anywhere that you will find the OEM piece. It is ordered directly from the factory and made for you. They run around $475 after shipping. I even called the company that makes them, they are the only supplier and wont sell to you directly. They do have 1 vendor who sells them, Axess Marine. They are on ebay but the price is a bit higher than JM.
I originally had a cheap one off ebay that was 160 bucks. It fit great and worked great but it wouldnt fit under the cover. I only trailer the boat with the cover on, so that was a major deal to me. Then by accident I bent one of the poles so I decided to spend the extra money and upgrade to the OEM. It is built a lot nicer. The fabric is thicker. It has 4 bows instead of 3 and contours the shape of the boat a lot better. It fits under the cover.
So basically...go spend the $475 with JMCamper. You wont be disappointed.