Do vestments (chasuble, stole, alb, amice, etc.) need to be blessed before used for liturgies? If so, where does the priest find the blessing for liturgical vestments?
Yes. Those should be in the Book of Blessings, which every parish ought to have.
It is recommended, but not required. The Blessing may be found under “Blessing of Articles for Liturgical Use” in the Book of Blessings. The central prayer is:
Blessed are you, O God, for making your own Son the eternal High Priest of the New Covenant and for choosing our own brothers to be the stewards of your mysteries. May your ministers who use these vestments, prepared for the celebration of the liturgy and set apart by your blessing, wear them with reverence and honor them by the holiness of their lives. We ask this through Christ our Lord.
Or a more general prayer may be used, which is:
Blessed are you, O God, who through your Son, the Mediator of the New Testament, graciously accept our praise and generously bestow your gifts on us. Grant that these articles, set aside for the celebration of divine worship, may be signs of our reverence for you and helps to our faithful service. We ask this through Christ our Lord.