Here is a link to Amazon but you can find it in most marine supply stores. There are several 303 products so make sure you get the protectant.
To prep the rail, you should wash them, remove any crud and then let dry thoroughly. Absolutely dry is necessary for the acetone to do its job.
Then wipe with acetone and rags, changing the rag or section of rag frequently as the acetone removes the oxidation. The acetone will dry quickly. You can do additional treatments if needed.
Finally apply a sealer/wax or protectant like the 303.
I have used Mop and Glow floor wax in the past. It works well but only last about 4 to 6 months depending on how sunny it is in your area. I use 303 but not on the rail so I can't comment on how well it holds up.
By the way, be ready for a surprise after you do the acetone scrub. Your rub rail may very well end up a different color and in a good way.