Belev Echad, somebody gave me “Mourning in Halachah” by Rabbi Chaim Binyamin Goldberg when my dad died. I will check in the book for you.
There’s no topic of listening to music on Lag Baomer in the index, but
according to Rabbi Goldberg (25:31) “During the entire twelve months of mourning, the mourner is forbidden to listen to a musical performance, even if it is not a celebration…”