Tips from Media Teachers
Here's a good one for old-fashioned black and white instructional films, government movies and all that kind of thing: https://archive.org/details/prelinger - Richard James, Cashmere
Dissolve has 3 free clips each month http://dissolve.com/free-clips - Katrina Sylva, Dargaville High School
Video Blocks has a seven day free download offer which seems to be always on offer. A maximum of 20 clips a day, so you could bring down a maximum of 140.
You need to register before downloading.