The events that occurred in India during 1857-1858 are referred to in a number of different ways. You need to take this into account when developing your search strategies.
Some resources, including Find It @ USC Libraries catalog and HathiTrust, use Library of Congress Subject Headings (LCSH). The most relevant subject heading for this topic is
Terms like Sources or Personal Narratives or Correspondence can be added to the end of the main Subject Heading to indicate that a book includes primary sources, such as first-hand accounts or letters.
In these resources, a Keyword search for the phrase "Sepoy Rebellion" will be very effective, since it will match the phrase included in the LCSH.
Different authors use different words when referring to the Sepoy Rebellion, especially in primary sources such as newspaper articles from the time.
Using the Boolean operator "OR" between similar search terms returns search results that include at least one of those words.
This is not a complete list, but below are some recommended options for finding primary sources on the Sepoy Rebellion.