This is the coolest frickin’ gadget ever, and it’s so rare, less than a dozen are believed to still exist. If you’ve got $6K to shell out, get yours here.
Short history from musicprintinghistory.org:
The Keaton Music Typewriter was first patented in 1936 (14 keys) by Robert H. Keaton from San Francisco, California. Another patent was taken out in 1953 (33 keys) which included improvements to the machine. The machine types on a sheet of paper lying flat under the typing mechanism. There are several Keaton music typewriters thought to be in existence in museums and private collections. It was marketed in the 1950s and sold for around $225. The typewriter made it easier for publishers, educators, and other musicians to produce music copies in quantity. Composers, however, preferred to write the music out by hand.
via Neatorama