I bought a pair from here https://dockingproducts.com/. So far good whips, but I have the older set and it is rusting a bit, think they have been improved since I bought them years ago. The best part of my style is they bolt to posts and can be straight up when needed to board and can be moved to the whip position.
The older mounts rusted a bit so I used Rustolium to renew finish. But I think the new ones are much better. I like them and they are doing fine. Do like how they tilt over from upright. I'd call the mfg. he is good to find more info on them. Holding up well.