Murakami-san lives up here in Kanazawa. He handed off the shihanke-ship to someone down in Yokohama a few years back. I haven't heard much from the school since. I know that there have only ever been a handful--as in less than the previously mentioned 15--of menkyo kaiden earned since the school's inception. I heard from a friend down in Yokohama that there are only a half dozen or so folks that train down at the Yokohama branch, and that they are all old and very high level.
There is a library up here in Kanazawa that Murakami-san donated all his books and scrolls to when he called it quits. He directed me there when I was inquiring into the ryuha. Stevens' book about Tesshu might shed some light on Muto-ryu, but gives nothing up-to-date. You may even be able to contact him personally if you want to get more info, Murakami-san also directed me to him. If I'm not mistaken, Daniel Lee mentioned some HIDEN magazine articles or contact info for the crew down in Yokohama. Contact him and see if he remembers the issue...
Good luck.
Matthew Snowden
-The only way to learn is be aware and hold on tight.