NoveList's got a brand new genre heading!
GN Celtic fantasy
This special subgenre incorporates the myths and legends of Ireland, Wales, Scotland, Cornwall, Brittany, and the Isle of Man; it also covers the Celtic diaspora, including the United States, Canada, Australia, New Zealand, and Argentina.
Celtic fantasy is related to, but distinct from, GN Arthurian fantasy, which focuses specifically on King Arthur and the Knights of the Round Table.
You can still use SU Mythology, Celtic to find books, but we thought this way might be more helpful.