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.
All Movie Guide: AMG.
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.