Materials that we generally think of as secondary sources--such as scholarly journals--can be used as primary sources if your aim is to closely examine a debate or conversation during a specific time period.
Here are some examples:
Remember, too, that JSTOR includes the deep backfiles of hundreds of scholarly journals. Suppose, for example, you'd like to see if/how American scholars in the 1930s were writing about Japan. By using the advanced search interface in JSTOR, you can limit your results to just articles from the 1930s and would discover that the journals Pacific Affairs and Far Eastern Journal provide numerous articles for examination.
Government documents can be rich primary sources. A few highlights: