The Franz Schmidt repertoire for the piano, left hand, includes not only
the Piano Concerto (released on a Pan CD), but a clutch of chamber works.
There's a Sony CD of the Piano Quintet, with an all-star cast (coupled
with the Korngold quintet) and additional recordings of the Clarinet
Quintet, which includes piano, on both Marco Polo and Orfeo.  All of
these are in print, as far as I know.  Alas, I do not have CD numbers
at hand, but I can research them and post them later.

The originals of all of these pieces were intended for Paul Wittgenstein.
For what it's worth, there are re-arrangements of all these pieces by
Austrian pianist Friedrich Wuerhrer, which spreads the keyboard part
across two hands.

Regards,

John Proffitt
KUHF-FM Radio, Houston