There’ll be some chilly lambs in Rome today!
For your St. Agnes needs: “Virginis Proles”, the Vespers hymn for virgin martyrs. It comes from Women in Chant…Virgin Martyrs, a Gregorian chant album by the Regina Laudis nuns.
Wikisource also has the words to the Lauds hymn, “O castitatis signifer” and “O Christe, flos convallium”. No music, though.