You could try emailing Horslips from their website: http://www.horslipsrecords.com/ - they're nice guys and would probably give you the lyrics no bother. Sorry I can't be more help; not much good on hymns, and a quick look at Ceolta Gael, both books, and Cas Amhrain and Croch Suas E, my usual sources, came up empty.

The other thing you might try is joining the Gaeilge-B maillist (google it) and asking there.