Hello Jules,
I know of a French family of minor nobility called the Baudard de Fontaine et de Saint-James. I thought it may be the family of which you speak. Firstly, the family is named de Fontaine, and secondly, received a title related to Saint-James, perhaps so-named for his services to the French King at the court of Saint James in London. I have taken the following passage from E. de Sereville's Dictionnaire de la Noblesse Francaise. Also, the Baudard de Fontaine family are still extant in France and several family members have their family trees posted on several French genealogy sites.
"Baudard de Fontaine et de Saint-James
Anobli par charge de Secrétaire du roi en 1713, comparant à Lyon en 1789. Baron de Saint-Gemmes par Lettres de 1755. Par jugement du tribunal de grande instance de Versailles, en date du 27 février 1973, l’état civil a été rectifié en Baudard de Fontaine, le nom de Baudard figurant seul depuis la fin du XVIIIem siècle."
I hope this might point you in the right direction.
Happy Holidays,
Christopher Barrios de Leon