I expect your university has copies of the Folk Music Journal. See Ian Spring's paper in volume 5, number 4, 1988: Why did 'the Bridegroom Greet'? (469-481). That will tell you all about the earlier song and some of its descendants, and will provide further references.

"Auld Robin Gray" (both old and new tunes) can be found in most older commercial collections of popular Scottish song. Pittman and Brown, Songs of Scotland I, 1877 (and many times reprinted), comes to hand, and there are plenty more. You need to be able to read music or make a midi file from notation, but if you are working on ballads for a further degree I imagine you can do that.