Primary sources are at the heart of historical research. Digitization of many historical documents has made gathering primary sources easier, but there is no centralized place to find everything. Locating appropriate documents 'of the time' requires exploration and effort.
Almost all historical subjects have a base of core primary materials that historians reference in their writing. But how do you find them?
Bibliography Mining
Find the recognized title of the source.
Once you have the official name of the document,
you can search just like any other printed source:
As a history student you are probably familiar with bound collections of primary sources that focus on a particular subject. These types of volumes can be very useful, but there isn't a 'source collection' for every subject you might wish to study. It is also important to not let yourself be limited to only those documents in the source collection. Often the joy of historical research comes from the obscure needle in the haystack.
As a history student many of your assignments may have started with a primary document. But as an historian, it will be your job to locate and incorporate primary evidence to support your unique historical argument. Entire fields of history have been created precisely because of a lack of primary documentation.
Write it down!
The discovery of primary documents can be quite serendipitous and unexpected. It is for this reason that a research diary is so important.
When you find something pertinent to your research, primary or seconday, make sure to make a note of it. You can always investigate it more later if you have time, but it is very difficult to retrace your path to discovery when you found your resource 'accidentally.'