Not sure if “registry” is quite the right word but I’m wondering if there’s such a thing as a list on a website somewhere that would tell you (or me) for which movies Your Favorite Actor (or Mine) has done a DVD commentary.
Sure, you could look up every movie he or she has ever done, but this would be quicker. And sometimes actors (and directors, producers, film historians, and other behind-the-scenes types) do commentaries for other people’s movies.