Today I discovered a wonderful webpage, dedicated to historical organ recordings.
It has two absolutely stunning and -in many aspects- historically very important recordings of Fritz Heitmann. First, the 1950 recording on the (then brand-new) Schuke-organ in the Gruft-Kapelle of the Berlin Dom with excerpts of Bachs Kunst der Fuge and second, the 1938 recording with excerpts of Bachs Clavierübung Dritter Teil on de Schnitger-organ in Castle Charlottenburg (destroyed in WWII).
There are also very rare and (to me) unknown recordings by Marcel Dupré, André Marchal and others.
http://ihorc.blogspot.com
Theo