You'll likely find a combination of scholarly and popular sources that talk about the film you are researching. To find scholarly research articles, you will want to look in academic databases. Film history is also documented online by a variety of reputable sources. Be sure to use a combination of sources for your project!
Each of these three databases will have scholarly research articles about specific films. Click open any of the databases and search for the title of the film you are researching in the main search box. You will see options on the left to narrow your search results further.