The Lelands link is dead, or at least it was for me.
Mail reply cards for movies were standard studio fare in the studio system period [1920s-1950s]. I have several, though none of the Babe. Here are a few examples:
One thing I've noticed in years of movie memorabilia collecting is that mail reply cards from the movie studios are often identified as generic photos or postcards, which makes the hunt that much more fun and rewarding.