www.bluegrasscollege.org is a free site that teaches bluegrass tunes! Click link below:
A link to a free download of Jay Ungar playing Margaret's Waltz (audio only). Copy and paste this link: https://jayungarandmollymason.bandcamp.com/track/margarets-waltz
A link to sheet music to Jay Ungar's version of Margaret's Waltz (scroll to bottom of page): http://jayandmolly.com/fiddler-magazine/