As of 10 years ago, Pianocorder cassette tapes were available from
QRS, as I recall.  I bought a bunch, and I'm sure that's where I got
them.  I don't think they appeared in the regular catalog; there was
a separate one.  I don't know what the current situation is.

I have some duplicates I'd sell and I know of someone in San Francisco
who kinda made a market and may still have an assortment, if he's still
alive and I can find his name.

Paul Eggert, Fountain Hills, AZ