I've been taking a course in Japanese history, and on the surface it seems that Japan skipped the Bronze Age. When the Yayoi period ended around 250 AD and the Kofun or early Yamato period begun, the people went from using lithic tools to iron tools effectively skipping the otherwise common bronze-step. Am I misinterpreting the data and if not; can someone explain why this is so?

edit: It seems I was wrong about this part. The use of iron tools started around the end of the second century, not the third. This means that it started near the end of the Yayoi period, not in the beginning of the Yamato/Kofun-period. end of edit

The logical conclusion would be lacking the materials, namely copper and tin, but we know of 2 minor tin-deposits in eastern China that were used in ancient times (China did have a bronze age) and several major deposits in southern Asia. As for copper we know of some larger deposits in China and at least one in Japan. To add; the Japanese imported culture and knowledge from the Chinese and Korean kingdoms before this time (and they imported iron from Korea as well), so they could have traded copper as well.

I hope someone here can be of assistance.