This is all in Japanese before anyone says I screwed up!!
Found this on youtube, showing the latter of Yamashita competitive career with some references to his youth. Introduced by his old rival and current heavyweight coach in Japan Saito-san, this is a look at the greatest competitive judoka of all time.
Having seen the whole thing though, I dont think he was undefeated. You can see he was clearly ipponed twice by the same guy (the monstrosity they call Endo!!) with the same throw, and although its now illegal, both of those should have been ippons, he was flat down both times.
That said, 202 competitive wins and undefeated in his entire career, olympic champion, numerous world champions and all-Japan with a tonne of other A-level tournament wins, flawless technique, and a true gentleman. Still active today in coaching kids and offering advice to the young heavyweights in Japan. I saw in a magazine here that there was an interview with Inoue Kosei and they asked him "who has the best technique of any Japanese judoka right now" and he said "Yamashita Yasuhiro", so they said, "no, not of all time, I mean, right now" and he said, "I know, its still Yamashita".
Great stuff, enjoy.