The oldest Seeburg piano I have has its original mandolin rail.
It uses the brass paper fastener that has the two legs that you
fold to hold them in place.  These are known as the ACCO number
ACC71502 and are sold at office supply stores.

The later Seeburg pianos used a fastener that is no longer
manufactured.  It was a Premier #2 paper fastener.  The last ones
that Player Piano Co. sold came from France (I think) and are no
longer available.  Nelson-Wiggen coin pianos used a piece of wood
as their mandolin.

Coinola and Cremona used a sliding rail with little wooden paddles.
I have seen some really early coin pianos with other types of mandolin
attachments.  The bottom line is there is more than one way to capture
the mandolin sound.

Don Teach
Shreveport Music Co.