GGC -
Primary source materials can be found in GGC's A-Z Database list.
Under "Types" use the dropdown menu to select "Primary source." The list of databases includes state and national newspapers, the Civil Rights Digital Library, Digital Library of Georgia, and Vanishing Georgia.
Other repositories -
You can search for archives with collections relevant to your research at ArchiveGrid
You can also use Google or another search engine, search for the keywords for your topic and try adding archives, papers, or special collections