Prepare to be a little disappointed with the range of tunes available for downloading.
When you can get 'round to it, invest in some of the "Voice of the people" range from Topic records. Most of the songs are croaked out by really old guys and gals, but it's excellent as a source of trad. material.
Or beg / steal / borrow / kill for a copy of Paddy Tunney's "Stone fiddle" album. (Vinyl or cassette only I think.)