Philippa,

I don't know how old the Kennedy/Petterson recording might be. However, I have a recording, actually an LP re-release I believe, of "Dia Luain, Dia Mairt", performed, in Irish, by Mary O'Hara. She is one of several artists featured in a multi-LP collection, issued by Capitol Records in the US in the early 1970s

I hopes this is helpful.

Robby