Try searching for a specific person or organization
You can often find primary source documents if you know the person or organization you're interested in. Start your search in Tripod and the sites listed here, but if that doesn't work, expand it to Google. Try using some of the document types (e.g. personal narratives, correspondence) as additional keywords in your Google search. Hopefully, you will find primary source documents that have been scanned by other libraries and made available online.
Need to identify specific people and/or organizations? Look at the Overviews page for suggestions. (Reference books tend to be useful for this purpose.)