Two wonderful sources for public domain film footage are available online
- Universal Newsreels: created between 1929 and 1967, these newsreels cover the major topics of the day. They were put into the public domain by University City Studios. (There are also many more recent pieces of news footage in this college.)
- Prelinger Archives: a collection of “ephemeral” film: amateur, advertising, educational and industrial material from a variety of government and commercial sources.
Try a search on “atom bomb” in either collection – in addition to several still-shocking film images, you’ll find the original “Duck and Cover” Civil Defense film.