Sources

I recently came across two great websites which contain hundreds of tunes available as sheet music, gifs, etc.

The first is Breizh Partitions, which contains tunes categorized by origin (Brittany, Scotland, Galicia, Wales, and Ireland) and instrument (accordion, bombard, bagpipe, flute, guitar, piano, and fiddle). I find many of the Breton fiddle tunes particularly beautiful and haunting.

Next, I found O'Neill's Music of Ireland. I happen to have this large and important reference book in my music library, but wish I had found the website first, to save the $35.

Musicians frequently tend to do things merely for music's sake and the folks who put together these websites deserve a lot of credit for their labors of love.