Depends which one you're talking about, of course.  If you're talking about the tune recorded by the Corrs, simply type erin shore into the very useful "Digitrad and Forum Search" box on the main Forum page for details of the piece and its real name.  If you mean loch erne shore (people often get confused over the spelling), then search for that; the material is here.  If it's something else entirely, then no doubt someone will know.

Malcolm