These are the 60s Match Game episodes that the Library of Congress has catalogued:
12/05/62 - the pilot
01/02/63 - Arlene Francis, Skitch Henderson
06/24/63 - Florence Henderson, Henry Morgan
08/20/63 - Faye Emerson, Henry Morgan
11/21/63 - Betty White, Shelley Berman
07/28/64 - Jayne Mansfield, Orson Bean
05/19/65 - Lauren Bacall, Roger Smith
06/02/65 - Joe Garagiola, Whitey Ford
09/23/65 - Jayne Meadows, Sydney Chaplin
I don't know if they have more than these 9 episodes. This is the first time I've ever heard that 50 number. If more do exist, God knows if they'll ever be catalogued.
I requested to view two MG episodes from this list last summer, for research purposes. It took them over 5 months to transfer them to digital video tape. The ones I requested were the 6/24/63 and the 8/20/63 shows. Henry Morgan was the highlight of both; not only was he funny, he was one hell of a 60s Match Game player! The 8/20/63 show has probably one of the greatest games from the surviving episodes, as it goes back and forth between the two teams. It ends with the winning team at $200, something Gene claimed was a record for the show at the time.