Rubrails are pretty durable, even if the no longer look pristine. (Good way to clean is with scotch pad or magic eraser). They will pick up dirt/rust when doing their job, but unless you are trying to restore your boat to optical perfection, I would try to re-attach them rather than replacing them.
Talk to D&R Marine, they may have the end pieces (shoes) that hold the rail against transom. If not, you could improvise with square tubing.