RTS rear shock
You can get a new noleen shock from noleen direct, though a bit pricey - have you tried the Risse route? They do 3 air shocks which offer a bit extra travel and are lighter than the noleen, but not original of course. I've got a noleen shock on an RTS 2 frame that has started to crack, though no idea whether it is still goo. Have owned from new, and has been sat attatched to frame in the shed since 1998.