I'm sure I'm not the first to come to this realization, but the scroll you find behind the banner in the dojo is of the Tiger Swallow style. This means that the only two characters we know of that could teach Ryo the move are Master Baihu and Lan f***ing Di. Either Ryo will meet another master (possibly in Bailou or Meng Cun) who can teach him the move, or he will have to learn it from one of the two previously mentioned villains. Was it that leg move Baihu uses before fighting Ryo? I seem to recall Ryo using it to defeat Baihu, but the game never tells you that you learned it, nor does anything happen with the scroll.