Also known as the Feast of the Apparition of the Blessed Virgin Mary of Mercy, for the Redemption of Captives. In England, Our Lady Of Walsingham is also celebrated on this day.
The Mercedarian Order (Order of the Blessed Virgin Mary of Mercy) has a proper Office for this feast. We have only found the text of these Hymns and so have set them to common Marian melodies.
Vespers Hymn, Dei Mater Virgo
Matins Hymn, Electa Proles Maximam
Lauds Hymn, Gaude Propago Candida
There is also a Proper Mass including a Sequence, Plaudat agmen captivorum. The complete Propers can be found here on pg. 221.
Note, Google will not allow you to download this book if you live in the U.K. etc.