Yesterday Mr. Mackin asked, "The current discs are a reddish-brown
brick color, smooth on both sides.  What is this material (celluloid?),
and where can I find a replacement or two?"

This material is red German pressboard, a very stiff and dense, but
thin, cardboard-like material, often iron red in color.  It is called
"pressboard" because it was used as a smooth, flat backup for the
printed sheet in a flat-bed printing press.

Pouch followers, small bellows stiffeners, reed organ 'vox humana'
rotating vanes, and even some small valve disks in Aeolian reed organs,
were made from this stuff in the old days.

Take a sample to an office supply warehouse, where many products there
are still made of pressboard.  A suitable replacement will be found
among document wallets, report covers (AccoPress), hanging folders, and
the like.

Richard Vance