I'm not sure how schools that are known for like Music with La Corda. Where the school is known for it's music branch, but regular students also attend. In this case the students wear 2 different uniforms based on music vs general. I'm guessing it might not qualify though.
La Corda D'Oro ~primo passo~ | Anime-Planet
Polyphonica's should get music school though:
Shinkyoku Soukai Polyphonica | Anime-Planet
Shinkyoku Soukai Polyphonica Crimson S | Anime-Planet
Also All-Girls or All-Boys might be another set of schools. Bodacious Space Pirates, candy boy, and love live school idol project, k-on would be good examples of all girls.... I don't know any for all boys so maybe that wouldn't be a relevant enough tag.