For Celtic dance music you might start at The Fiddler's Companion. Thousands of tunes are listed with published sources, and if you click on "tunes" you will find links to many sites offering tunes in a variety of formats - GIF files, MIDI, ABC etc.

French traditional dance music, as heard at sessions in south and southwest England for instance, is perhaps a little easier for starters, though a bit more rhythmically complex. But maybe you're looking for classical tunes, or something else. If you would like to be more specific, I might be able to provide appropriate links.