I have now finished the typesetting of the other Büttner autographs I own:
Serenade in 3 movements for 2 harps op.40 (1929)
Der Totentanz (Ballade nach Goethe), for reciter and harp op.20
Both scores remained unpublished so far, so the publication on my website is the first chance to study the pieces. So can get scores in pdf format here (and by the way for free!):
http://www.tobias-broeker.de
Best,
Tobias