From an interview with James Gardner for the podcast, “Your Story, Your History”

Getting autographs of most of the stars in The Wizard of Oz was easy -- Billie Burke and Margaret Hamilton were ON the set of the Munchkin village, but the big prize was getting Judy Garland’s picture. That was another story and an odyssey for me because it involved crossing parts of the building where I was not supposed to be, day after scary day.

The full story is in Chapter 2 of the book.