Surely Architectural Millinery IS at MOMA. When I was a curator there, I programmed it several times, including an exhibition which ran from June 5-8, 1981 entitled "Films Made in New York City: From the Archives".
If you can't rent it through the Circulating Film Library, you should make the request to the film archive. It was shot in 35mm. I think it has been preserved in 35mm; I don't recall if a 16mm reduction print was made for it, but I believe there is a 35mm duplicate print.
It's a quite unknown and really charming Sidney Peterson film in which he compares the shapes of hats the denizens of New York City wear with the forms of the city's rooftop buildings. The narration is by Henry Morgan. As I recall, the film was produced by The Museum of Modern Art in the early 1950s.
Highly recommended, for the linkage in both formal and witty fashion between human beings and the city's architecture.