I've never seen one. We used to have special blackboards (are we allowed to say blackboards these days?) in the music department with the lines permanently drawn on them. I don't remember doing music anywhere other that the music department, so I don't suppose that we needed one. The music department was, by necessity, on the outer edges of the school campus, particularly useful for those of us who made rather unpleasant noises with stringed instruments.

It sounds like an interesting invention, although everything musical seems to be done with overhead projectors and photocopied sheets in the schools that my children have attended.