When searching any database (the library catalog, article databases, web searches) the following terms will be useful:
The following links will take you to registration pages for various listserve groups focusing on theater and film.
The Encyclopedia of the American Theatre, 1900-1975 REF PN2266.B68
The New York Public Library Performing Arts Desk Reference REF PN1584.N49 1994
Theatrical Design in the Twentieth Century REF PN2091.S8T47 1996