Modern Hagiography
Lives of the Saints by Alban Butler.
Lives of the Saints by Sabine Baring-Gould.
Contemporary Hagiography
Mention in Gregory of Tours’ History of the Franks, Book 3.15 and Book 3.19.
His life is in Gregory of Tours’ Lives of the Fathers (may be borrowed for free, with registration).
An epitaph for Saint Gregory of Langres written by Venantius Fortunatus (only available open access in Latin, but it is not long).
Nihil sub sole novum 