I was trying to transcribe a melody for one of the obon dances from a crappy recording. Finally decided to look to see if I could find sheet music anywhere, I stumbled onto this. Don’t know if people would find it particularly useful, but it is a massive collection of folk melodies transcribed into western notation from the turn of the century (one of three such collections made between 1890 and 1920, from what research I can find - Nagai and Kobutake did a similar one in the 1890’s as well). This one just happens to be fully digitized.
For what it is worth.