The Hamada pistols were two of the few examples of Japanese military arms made by private companies rather than government arsenals. Hamada ran a shop making sporting arms before the war (and after), and converted his production to a .32ACP blowback pistol of his own design for the military to use. It was a successful project, and the result was a request to redesign it for the 8mm Nambu cartridge. After a few back-and-forth sessions with ordnance officers the new design was accepted and a separate factory outfitted to produce it.
Hamada pistols are very scarce today, as most of the 7.65mm ones appear to have been sent into China. The only surviving 8mm Hamada pistols known are in the white with serial numbers below 50, suggesting that they came from a preproduction batch. The regular ones appear to have been lost at sea in transit of destroyed by American bombing before being issued out to troops in the field.
I was able to take a look at examples of each type, and took these photos (click to enlarge):
7.65mm Hamada (aka, Type Hamada):
8mm Hamada (aka, Type 2):