I haven't.

As I understand it, "Tam Lin" began as a ballad in its familiar form some time in the 18th Century. Burns printed a text and tune, which he claimed to have got from tradition. As far as anyone knows, he was truthful about distinguishing traditional songs from his own creations. However, there were few reasons of art, conscience, or economics in those days to keep a literary fellow like Burns (who was also a genuine "trad singer" as we'd call him today) from overhauling a text and tune to improve it, with or without acknowledging his own efforts.

Burns songs were so popular, and cross-fertilization so easy, that any traces of "Tam Lin" collected over the past 200 years may owe something (or nothing) to his "definitive" version.