The Keaton Music Typewriter is a rare found. According to CBS News, "There are fewer than a dozen known to exist". This bad boy will make it easier for you to write your music, compared to writting it out by hand. Just think how much time you could save. Since they are rare a username jackredbarn on Etsy has one available for sale. But don't expect it to be cheap.
A little 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.
For more information: http://www.aquaporin4.com/etcetera/ETC.25.pdf