Hi,   The short answer is, I'm sorry, we can't remember yet. We will let you know if we find the source material.
The old brains are sorting through files of memories. We would have learned it from recorded material, though, in the 1980's or early 1990. We both seem to be hearing it played on uillean pipes and fiddle.
In the 80's we lived in a 21 foot sailboat we built, on the Ohio River. We had a radio and picked up Fiona Ritche with Thistle and Shamrock. The little boat drifted in and out of radio reception with the wind. If the wind was down, we recorded some tunes to learn. Those old tapes are sort of a background noise in our brains, may have learned it there. Also may have altered it some between the learning and the playing; between the thinkin and the doin.   Around 1990 we met Tim Britton at Kentucky Music Week. We were set up with our tipi as buckskinners, with our ocarinas and pocket pipes. Tim was playing pipes on the hill behind us. David got up and walked over there in a trance by the sound. May have learned it from Tim. After that pipes crawled into our ears, and ocarinas became a way to access pipe music. I worked on the design of the pocket pipes ocarinas until they would play those tunes, with the right intervals and harmonies. Also highland pipes are generally confined to the same 9-note range, so the tunes need not be altered to fit. We sat for hours and days at festivals playing ocarinas and hunting tunes. Some tunes go in one ear, get stuck awhile, and then come out the whistle. Some of them come out altered.