There isn't a perfect search method for locating screenplays, especially of adaptations. In many cases, you can search the film's title or screenwriter name (NOT director) and browse the results for a screenplay. For popular titles, it may be more effective to conduct an advanced search and exclude the keyword videorecording. A subject search for Television scripts as well as Motion picture plays will show quite a few available in CLIO. A subject search for Motion Picture Plays > Bibliography or Television scripts > Bibliography leads to lists of published screenplays.
Free resources on scripts. While these are fairly reliable, the sites can have ads and authenticity/copyright are not as certain.
Searching by subject "Motion Pictures Pictorial Works" brings up books with film stills in them at Columbia/Barnard.