I can't retrieve it at the moment since I'm away from home, but I believe Adam Nedeff's "This Day in Game Show History" listed all of the hosts in it and it is at that number plus. You could have a marathon of substitute hosts alone!
Just looked it up myself, and there were twenty-three hosts in total: Mike Wallace, Bud Collyer, Ralph Bellamy, John Cameron Swayze, Sonny Fox, Robert Q. Lewis, Jim Fleming, Merv Griffin, Gene Rayburn, Orson Bean, Bert Convy, Mark Goodson, Garry Moore, Peggy Cass, Bill Cullen, Joe Garagiola, Robin Ward, Richard Kline, Gordon Elliot, Lynn Swann, Alex Trebek, John O' Hurley, and Anthony Anderson.