I tried writing him a messege on his YouTube account with my very basic Japanese, and got a reply, but it didn’t quite answer my question of where you could obtain these instruments. I think the hint is that he is restoring them himself, and playing them, and that might be it. So unless he decides to start selling them, that might be a dead end for now. Mind you, I enquired about the Reikin at the time, so I should probably ask him about the Dai-Kokyu too.
What I am not sure about is if the Dai-Kokyu is an instrument he has recreated, or one that is as available as the regular Kokyu. I will need to Google that a bit more. I agree I like the sound of the Dai-Kokyu much, much better then the regular Kokyu.
If it turns out that the Dai-Kokyu is also a recreated instrument and obtaining one will be very difficult, then at least I can work on bowing a Shamisen. I think that would be somewhat close to playing a Dai-Kokyu. But should the Dai-Kokyu be available, I will have to save up for one. But just the same, I think bowing a Shamisen would be interesting too.
I find it so amazing how much this topic has grown! I really appreciate your insight on the topic Julian. I think Japanese traditional instruments are great, too. Down the road when I get comfortable with the Shamisen, I would love to work with the koto a bit too. I also have a little bamboo flute, but I have no idea if it is Japanese or not.