Wow, that's a sweet machine. I don't have any info about it, I just wanted to say that I'm a little envious, even despite owning a pretty capable knee mill.
I can at least relate to owning mysterious Japanese tools, as my mill has a similar story. Made in Japan sometime in the 60's and there's basically no documentation available. I've found photos of two others online.
The good news is it looks like a well cared for and robust machine. I doubt you'll have any need for parts as long as you treat it well. On my to do list for my machine is repairing the fine feed gearbox on the side of the head, of course I have no parts diagrams or lists available so it's going to be a challenge.