Alan Stivell wrote a Celtic symphony but the main proponent of this type of music is Michael O'Sullivan - I think he's professor at the University of Limerick ( or is it Cork ?) Some one out there knows exactly I bet. There is Video called River of Sound which charts traditional music and dnace development. I think there is also a CD of the same name.

There are other celtic/ classical music composers - none of which I can remember. Allegedy O'Carlan ( Blind Irish 17th/18th Century Harpist) wrote his concerto when challenged to write in that style.

Hope that is some help and others can build on this.

Julie