I have found some material that may work for Scotty Greene's Cremona
valves.  It is a stiff, paper-based material made by the ACCO company
as covers for stacks of computer printouts.  The material I have is
0.018" thick and is blue but I have also seen it in brown.  Sometimes
it is called ACCOpress.  I got it at my local Office Depot store.

I have found that discs can be punched out with an arch punch.  I used
it as an interface layer when I glued my Duo-Art pneumatics back on so
the next rebuilder will be able to get them off!  I have enough left
over that would probably do the entire job if Scotty cannot find it
locally.

Pat DeWitt
Fort Wayne, Indiana