Well, they are, in fact, in Hymn Melodies for the Whole Year - but for July 2, which apparently was the former date of the celebration of this feast (something I'm going to have to look into, in fact!).
(EDIT: Wikipedia says this:
This feast is of medieval origin. It was kept by the Franciscan Order before 1263 when St. Bonaventure recommended it, and the Francisian chapter adopted it. The Franciscan breviary spread it to many churches, but it was only universally adopted in 1389, when Pope Urban VI extended it for the whole Church, to be celebrated on 2 July, a date that was kept in the Tridentine Calendar. In 1969, Pope Paul VI moved the celebration to 31 May, between the solemnity of the Annunciation of the Lord and that of the Nativity of St. John the Baptist, "so that it would harmonize better with the Gospel story". In the Anglican Common Worship, the date of 31 May is adopted, although the 1662 Book of Common Prayer has the 2 July date.
And the May 31 date does make more sense. According to New Advent, "Assuming that the Annunciation and the Incarnation took place about the vernal equinox, Mary left Nazareth at the end of March and went over the mountains to Hebron, south of Jerusalem, to wait upon her cousin Elizabeth....")
Here's the lowdown: "On the Feast of the Visitation of the B. V. Mary (July 2) & during the 8ve (when the Service is of the Feast)," the hymns are:
For Vespers: Festum matris gloriose, which LLPB's book of hymn names lists as "Now in the holy celebration," and which is in the Hymner, translated, at this page. Here is the chant score:
For Mattins: Mundi salus affutura - "Portal of the world's salvation." English translation in the Hymner here, and here's the chant score:
For Lauds: O salutaris. Honestly, I'm not sure what is meant here; "O Salutaris Hostia" is the only hymn I know that begins this way, but it doesn't seem appropriate for this feast - and I don't recognize the tune (which doesn't seem to be in the right meter, either). [EDIT: The hymn is O salutaris fulgens stella maris. I found, in this issue of The Dublin Review at Google Books, this entry about this hymn:
The hymn at Lauds is written in Sapphic verse, and is, in its way, no leass beautiful than the former. The poet begins by invoking that "bright and guiding ocean star which brought forth the Sun of Righteousness."More at the link. Here's the chant score:O salutaris fulgens stella maris,
Generans prolem veritatis solem
Mater bonorum clemens famulorum