Much of the Hohner spoon gasket material was 1/16th in cork sheet

Try an auto parts store. Barring that try .060 Inch gasket material

Use contact cement

FIXED! Found some thin cork at crafts store, already had contact cement. After I had put the cork on I very carefully bent the spoons down - it didn't take much - they are perfectly flat now and work fine. :)

Thank you to everyone who gave me advice on this thread! Now comes the hard part - actually incorporating my left hand into the mix. lol.

You're welcome.