Mitchell,
I had the same problem with my CS80 several years ago. I ended up making one that looked ok and would have been great if I had a band-saw (or just got a plastic/metal supplier to cut it for me). I got the outline and cut it from clear Plexiglass and made the bottom rail from some aluminum channel from a hardware store and some random hardware for the pins.
I had some very nice folks from this group send me detailed photos and dimensions of their music rests as reference.
David
I own a Yamaha EX-2, and the music rack/stand/rest holder piece is missing from it. The music stand holder is the round nickel-plated piece in which the music stand should sit, as in these pictures of a EX-2 and SY-1: