I bought it at Mejiro. If you want to invest in the real deal, this is a good choice in my opinion unless you have some contacts and/or speak Japanese. Even then, I don't think you will be saving money.
Mejiro have instruments by a variety of makers and perfect English skills to answer your questions and chat.
They were very happy to let me try as many shakuhachi as I liked until I was ready to choose.
My instrument was made by Shomei and is 2.39. (Don't ask me to explain that, but shakuhachi means 1.8 in some ancient measuring system).
Here is an example of a Shomei flute.
Mine is not that big, but it's quite a bit longer than the one I first learnt on.
I found some more information about Kobayashi Shomei on a blog, but it is quite an old post and the blog seems to have gone quiet so I'll quote from Shakuhachi Stuff here:
It was in 2007 when I met him for the first time. He struck me as a living komuso because of his austere spirit. He traveled worldwide when he was young as a backpacker. He draws paintings every month on komuso and his paintings reveal his inner spiritual world. (He was once accepted to an American university to study art).
One day, when he allowed me to play his (and his friend's) vintage flutes, he scolded me and said: "I don't understand what you are trying to get from each flute. This precious moment won't come back aqain. Why don't you put all of your energy into each flute?" Since then, he became my good friend and mentor. Later, he explained that he had done research on kokan vintage shakuhachi, and the only useful way for him was to play them with the maximized energy for a few hours at least, not by playing lightly or measuring the bore shape, length, and size of those flutes. In other words, he embodied the characteristics of each flute.
Kobayashi is predominantly a jinashi maker, even though he gives shakuhachi lessons regularly at Mejiro. Among the many jinashi shakuhachi that I've tried, his flutes are most colorful and flavorful in terms of tone quality. I particularly liked his long flutes. The sounds of these flutes were profound, vibrant yet light and smooth. As a pianist, I always think of his jinashi as Steinway, whereas other makers' flutes, however functional and playable, sound like the Yamaha or Kawai to my ears. Of course, this doesn't devalue their flutes (I have theirs and love them). But the tone quality of Kobayashi's flutes is outstanding.
At the moment I am finding walking and playing good for improving my technique.