Primary sources can be such a wide range of document types, from newspaper articles to letters. There is no comprehensive website for finding them. Here are some suggested starting points.
These links may be helpful for finding primary sources (produced by the US government) that aren't included in the DNSA. If you have any difficulty searching these, talk to Sarah for assistance (selichk1).
There are many websites offering digitized versions of primary source documents pertaining to Latin America. Here are just a few options. Talk with a libraran to find others.