| The plentiful rifles you mention all are imported in large batches from long-term storage facilities in countries that dipped them in cosmoline and put them away at the end of their service. At some point it was decided that they are no longer useful for current military practice and put on the market. When that happens there are LOTS of them available.
To my knowledge, at the end of WWII the Japanese were almost totally disarmed. No such stashes were created, the few that come on the market come from private collections. (It would be cool if I'm wrong and a batch of 10,000 was discovered but I'm not counting on it.) |