Rub rail end caps
Alcast Foundry in Redondo Beach, CA may be able to make it for you............if you have the old one even if is broken. It will be a solid casting and will need to be polished and anodized. Another long shot is Taco Marine. Some West Marine stores have a sample "ring" and you could see if anything will work. Another long shot is Garhauer. They might be able to make it out of stainless.