What kind of authenticity you looking for if you don't have personal friends staying in Japan where you can bunk in with them? Tourists want homestay but all homestay are required to abide rules and regulations and apply for license etc. All these result in "commercialism" lor?
It's always a double edged sword. I find it puzzling that people want homestay yet complains about "commercialism".
Then stay in hotels and save on paying the premium for homestays in the middle of a village where the locals themselves do not stay. Once the tourist buses leave, most of the locals would leave along with them except for the few using their homes as "homestays"