There are a number of ways to find reviews of films:
Google. Search for the film name and review. For example, rocky horror picture show reviews
Databases for Film Studies. The databases listed here all include film reviews.
New York Times Film Reviews. Covers 1913-2000. Reference PN1995 N4.
Library Catalog. Select the Books & Media option. Then pick Subject from the drop-down menu. Search for motion pictures reviews. Examples of sources you will find include:
Carr, Jay, ed. The A List: The National Society of Film Critics' 100 Essential Films. Reference PN1995 A33 2002.
Kauffmann, Stanley. American Film Criticism, from the Beginnings to Citizen Kane; Reviews of Significant Films at the Time They First Appeared. PN1995 K293.
The Motion Picture Guide. covers 1987-1999. PN1995 N346 1987.