You're right: it's not easy to find a photo of Mr. Sorel online.

I can find only one. In a 1979 New York Times article
(available from the NYT web archives, but unfortunately
not for free, there is a fuzzy photo of a scene from
WNET's 1976 historical drama series "The Adams Chronicles",
third episode: "John Adams, Diplomat", with Guy Sorel
in costume in his role as the Count de Vergennes.