Honestly, I go off lists I find on Google. I usually search things like “18th century French names” or “old French names” and see what I can find. And since I know finding era accurate names can be a struggle, I really don’t ask that the names are 100% time accurate, just preferably not more common, modern names. I also know a lot of French names a few centuries ago were often derived from names in the Bible, so I could suggest: Marie, Jeanne, Catherine, Magdelene, Blanche, Françoise, Anne, Jacques, Gaston, Louis, Clovis, Adam, Béranger, Hubert, and Hippolyte for first names. As for surnames, maybe: Lavicomterie, Osselin, Beauvais, Duplantier, Laignelot, Desmoulins, Grangeneuve, Deleyre, Renty, or de Boissy. And you can always look up names of French people in the 18th century on Wikipedia and pick a first or last name from there(I did it for a few of mine). There is also this list with a ton of different links to reports or articles about French names(although much older, those name can still fit).