What sources have authors used to write their articles/books (your secondary sources) about the Cold War? Are any of those sources available to you?
Visit their home pages. Have they digitized materials? If they haven't digitized, have they published Finding Aids (which give you a good sense of what materials are contained in their collections)?
When searching a database of books, whether the catalog or Google Books or WorldCat:
Think about the people associated with your topic. Did they write an autobiographies? Are their speeches or papers collected in a monograph? One obvious example: who was the President?
Examples of a couple searches are below: