When I've heard Daithi perform the song live, he tells a story that the song is either quite ancient, or possibly 20 years old. ;-) I can't quite recall where he found the song, but it seems to me he got it at a summer college in Co. Donegal. While many hymns are over a 100 years old, most which have survived in Ireland have been composed more recently.
As to the CD--I had the chance since yesterday to check the web for it. Green Linnet only has it on cassette. However, Amazon has it one CD for (if I'm remembering correctly) around $22.00!!! Ouch!