My first thought is that there is so much Celtic music on the Web (for free) that this is the first place I would recommend.

Tunes at Ceolas is an excellent site with more tunes than you could poke a bow at. There are lots that you can simply print out as GIF's, others in Acrobat format that you can print if you have Acrobat Viewer software (downloadable for free) and thousands of tunes in MIDI or ABC formats that can be played on free software, or printed using inexpensive Shareware. Sorry but I don't have the URL, but it is very easy to find.

Regards
John