taken from http://ca.geocities.com/spacephysicsisu/meteoroid.html#composition
It seems a meteor would contain the proper material for forging a blade, and even to an educated modern day person the idea of having a blade forged from a meteor is intriguing to say the least. If I was a very wealthy person I would love to have a blade forged from a meteor, as a way to set it apart as wel as conversation if nothing else. To a person living centuries ago it would surely be a priceless treasure to have a blade forged from the very material of the heavens. It's this reason stories like excalibur have captured our imaginations for generations. While perhaps not commonplace, and perhaps not even in Japan, I am sure this type of thing took place. I think it would require immense wealth to have such a blade forged, and that type of wealth was not something a typical Daimyo or at times even the emperor had.
The only thing I am not sure of is just how easy it would be to remove impurities from this type of Iron. After enduring the conditions of frozen space then going through extreme temperature of the earths atmosphere what type of chemical changes took place and did the impurities bond in some way to the iron? This is just speculation, I know nothing of metallurgy or geology, or of sword forging for that matter. I just found this an interesting topic.