The Archives Wiki is a website, sponsored by the American Historical Association, that offers information about archives around the world, organized by location. Coverage is spotty, since the website depends on user contributions, but it will help you locate repositories in your area.
Perhaps the majority of primary sources are available only in repositories—places that collect, catalog, and preserve sources. Libraries and archives are the most common types of repositories, but you may find others with sources for your topic.
Check the Internet first to find repositories and see what they hold. You will probably find at least the address and contact information for most repositories online. You may also find information about a repository's holdings online. Nearly every library has its catalog available online. Many archives will describe their collections and provide finding aids for some of their resources. By checking a repository's website, you can get an idea of what it has to offer you. But some repositories may not have a website: you would be wise to check print directories for small or specialized institutions that are not online. Two such directories are the American Library Directory (020 Am35) and The Official Museum Directory (069 Am35o).
The following types of repositories might have sources on your topic:
When looking for primary sources, though, you almost always should contact the repository's staff directly. Many collections in archives go uncatalogued, so frequently they are not described on an institution's website. Calling or e-mailing the repository's staff might make you aware of sources that you otherwise wouldn't know about.