The film was made in 1956 by Norman McLaren and Evelyn Lambart for Canada's National Film Board. McLaren, a Scottish-born Canadian, pioneered the use of stop-motion animation of abstract shapes synchronised with sound, using the same technique adopted 25 years later by Rod Lord for his seminal work in producing the animated book sequences in The Hitch-Hiker's Guide to the Galaxy BBC Television series.
In early 2001, I purchased from the NFB a copy of Rythmetic on videotape. However, it was not until this month that I had dug out my VCR and transcoded the video to digital form. The result of this encoding is below. Given that the original is a publicly-owned work, I see no reason it should not be made available.
Update: This is the high-quality encoding. It is much superior.
The official page on this video contains interesting information, including production photographs showing Mr McLaren creating the animation.