Hello BostonW8350!
You are probably talking about Saint-Samson-de-la-Roque (49°*25′*43″*nord, 0°*25′*54″*est). Do you happen to know if your father was shot down by Flak or had some kind of malfunction (engine failure, engine fire on board, etc.) that resulted in his crashing?
It is possible, but am not sure if this document is available, to find the RAF Crash Report for W8350. Someone can lead to that document.
The book "JG 26 War Diary, volume 1", by Donald Caldwell do inform on page 268 that on the 17th August 1942, this Jagdgeschwader had 4 scrambles, resulting in 6 Spitfire claims (mostly against 401, 402 and 602 Squadrons), without losses recorded. The author do inform that JG 2 "Richtofen" scrambled earlier and sustained one loss against the B-17s of the VIII AIR FORCE, without claiming!
Hope this help your research. I do know that Historians Jean Louis Roba and Eric Mombeek had written War Diaries (Books) about the JG 2 "Richtofen", which I do not have. Perhaps someone do have those books and can add more for you, regarding that particular day you are looking for.(
https://www.amazon.com/Dans-France-3.../dp/2930546085)
Most humble and sincerely yours
Adriano B.