The only other Tsunoda Saturns I can find by googling seem to be in Japan, as I found them on what seems to be a Japanese blogging website. I feel like this might be a pretty rare bike to see in the US.
For what its worth, the closest example to mine that I found was a few cm bigger than mine and the owner said their's was Tange 2. Just a little more possible support for the Tange 1/2 guess.