The Daibukan, or Great Book of Heraldry, is a gigantic secondary source on Japanese heraldry from the 1930s. I’ve gotten to look at it before, but it wasn’t until recently that I learned that a scanned copy is available from the NDL online. The right half of page 55 (as the online version numbers things) is the end of 1591, and the left half is the start of 1655, for those interested in SCA documentation.

It itself compiles various earlier books of heraldry. One is the Kamakura Bukan, also available online, which documents the heraldry of the Kamakura Period (1185–1333). Another is the Ashikaga Bukan or Ashikagake Bukan, likewise available online, which documents the heraldry of the Ashikaga Shōgunate (1336–1573).

While perhaps not as badass as period sources, Daibukan has lots of interesting mon, and I’m happy to have easy access to it.