There were two major Nambu variants, the 04 and the 14. I can't really remember which was which, but they were not, by any stretch of the imagination, great pistols.
There was also a Type 94, which is widely called the Nambu, but I don't think it had anything to do with the commission that designed the original Type 04 and named for the Col. who headed up the design committee.
Adequate at best, which is OK, because the Japanese didn't view handguns as fighting weapons, but more as badges of rank, not unlike the sword.
8mm Nambu ammo is available, but it is NOT common, and not cheap, either.
Try Old Western Scrounger.
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Beware the man with the S&W .357 Mag.
Chances are he knows how to use it.