Japanese Nambu pistols used to be widely ignored as inferior and uninteresting, but prices have been climbing in recent years (as with all Japanese wartime arms). As prices rise, it is beneficial have as much information as possible about the guns, to ensure you are getting the gun(s) you really want. Happily, there is an outstanding reference work on Japanese pistols available: Japanese Military Cartridge Handguns 1893-1945, by Harry L. Derby III and James D. Brown. It covers the two major Japanese WWII pistols – the Type 14 and Type 94 Nambus – is great detail, as well as having chapters on a bunch of much less-known handguns, including the “Grandpa”, “Papa”, and “Baby” Nambus, the Mark A experimental Nambu, Hamada, Hino-Komuro, Inagaki Shiki, North China Type 19, Sugiura Shiki, and a variety of flare pistols.
This book really is the one-stop shop for Japanese pistol information – nothing else I’ve seen comes close to matching it.
However, if this volume is simply a lot more information than you want, I would suggest James Brown’s abridged version, Collector’s Guide to Imperial Japanese Handguns. It is about a third the price, with about a fifth of the content (see our review of it).