You are allowed to use internet sources for your final paper. There are many good sources available, and these are some of my favorite reliable sites--each of these is hosted by a non-profit theatre group or library.
McCarter Theatre study guides
Guides to plays performed at Princeton's McCarter Theatre.
The New York Public Library for the Performing Arts
One of the four research branches of the NYPL, with digital collections, finding aids, research guides, and more. (See in particular the Billy Rose Theatre Collection).
Online Archive of California
Digital library collections from universities and museums throughout the state.
Los Angeles Public Library digital collections
Various images including film posters and fashion designs
Library of Congress Theatre/Dance collections
Exhibits and images of items at the Library of Congress