Find Plays 
Like most books in the CalArts Library, playscripts are organized by Call Number within the Library of Congress Classification (LCC) system. Playscripts can be found throughout Class ‘P’ of LCC, but there is no "special section" for them beyond that; they are grouped in with prose fiction, poetry, and other creative literature, organized according to the geographical origin of the language in which the play was written. Here's a partial list:
PA: Classical Greek and Latin Languages and Literatures
PK: South Asian (Indo-Iranian) Languages and Literatures
PL: Languages and Literatures of Eastern Asia, Africa, and Oceania
PQ: French, Italian, Spanish, and Portuguese Literature
PR: Literature of Britain and former British colonies
PS: American Literature
PT: German, Dutch, Flemish, Afrikaans, and Scandinavian / Nordic Literature
Plays are often collected in anthologies; The Play Index, INTER-PLAY, or a print index will give you the title of the anthology or other source in which the play can be found. To search for plays by type of cast or genre use The Play Index and/or New Play Exchange (NPX).
Need more help? Reach out to your Performing Arts Librarian, Sam Crawford (scrawford@calarts.edu).
Drury, Francis K. W., and James M Salem. Drury's Guide to Best Plays. 4th ed. Metuchen, NJ: Scarecrow Press, 1987.
Harvell, Tony A. Index to Twentieth-Century Spanish Plays: In Collections, Anthologies, and Periodicals. Lanham, MD: Scarecrow Press, 2000.
Montgomery, Denise L. Ottemiller's Index to Plays in Collections: An Author and Title Index to Plays Appearing in Collections Published Since 1900. 8th ed. Lanham, MD: Scarecrow Press, 2011.
Samples, Gordon. The Drama Scholars' Index to Plays and Filmscripts: A Guide to Plays and Filmscripts in Selected Anthologies, Series, and Periodicals. Metuchen, NJ: Scarecrow Press, 1974.