Use Keywords Wisely
A keyword search (in Tripod, JSTOR, and other places) can turn up published primary sources. Try entering terms like "correspondence," "diary" or "diaries," "broadsides," "records" and "documents."
Try Subject Headings
Librarians assign subject headings to describe published works. You'll see them in Tripod records (example).
Here are some words to look out for in Library of Congress subject headings (the kind used by the Trico Libraries) that will alert you to possible primary sources. These subheadings include:
1. Search for your topic in Tripod (e.g. "East India Company").
2. Under the "Books and More" search results, click "More."
3. Under "Narrow Search" (at the right), try these different limits (one at a time). The links change based on the search results, so you might not be able to try all of these limits for a given search.