How far are you from Nagaoka, Kashiwazaki or Takayanagi? Too bad that you're presently immobile, but keep your options open next time you have to go to Tokyo. There are places to go for sampling which are much more reasonable than going into a bar or buying a full bottle.
I've only been to one sake plant, in Mashike, Hokkaido and have always wanted to go to more.
I guess one of your best bets then is the 180ml. bottles that you should be able to find in Niigata or Nagaoka. During my last trip I always had one in my pocket and that was how I became acquainted with Yoichi 10, Bowmore 12, Hakushu NAS, Hakushu 10, not to mention a few unmentionables.