If you are researching a particular play as it has been represented in film, try a search for the name of the play AND the word film (i.e., "romeo and juliet" AND film)
Sample search in CONSORT:
Shakespeare AND film as KEYWORD.
Sample search in OhioLink:
Shakespeare AND film as KEYWORD.
Be sure to check the bilbliographies of the books, chapters, and articles you find for even more resources.