Sarantis’s name day is March 9, the feast of Forty Holy Martyrs of Sebaste.
Churches that follow the Old (Julian) Calendar keep the same feast on March 22 of the civil calendar. See everything commemorated on March 9.
The saint behind the name

Forty Holy Martyrs of Sebaste
March 9, Martyr, Σαράντα Μάρτυρες
The Forty Holy Martyrs of Sebaste were Roman soldiers who confessed Christ in Armenia in the year 320, during the persecution of Licinius. Refusing to deny the Lord, they were condemned to stand through the night upon a frozen lake, with warm baths set on the shore to tempt them. One gave way, but a guard, beholding crowns descending upon the martyrs, confessed Christ and took his place, completing the forty.
Name days: Sarantis
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.