I remember them, I still have one. I've got four electric chairs which I keep in working order, paranoia over breakdowns I suppose!
I was in Johnston's a bit over a year ago in my vintage E&J Premier, the owner was amazed to see one. He told me if I ever need parts for it that he had plenty including complete frames. He just might have a used Marathon, or necessary parts. Ask to speak to the owner though, the help there won't have a clue as to what you want. You could try CIL but don't hold your breath.
http://www.johnstonmedicalsupply.com/http://www.cilberkeley.org/