19C America is...definitely not my tarmac...but here is how I would start if I were you. Get a couple of secondary sources on your subject--academic books (i.e. from a university press) focused as closely on the war as possible. Then comb the bibliography relentlessly. You'll most likely come up with some thing that are archival sources rather than published, so you won't have access. But surely you'll turn up some diaries and "Collected Sources" type anthologies as well.

Books are a given, but keep in mind that primary sources include things like speeches, photographs, laws, first-hand accounts, etc. If I were you, I'd try periodicals like magazines and newspapers. For example, the Library of Congress lists several prints published in Harper's Weekly in 1877. You can likely access this periodical through your university library. You can also access historical newspapers, which often include first-hand information. You may have digital access, or maybe you'll spend quality time with a microfilm reader. To get a feel for what kind of information this will yield, see here. Finally, you can likely access digitized books through Project Gutenberg or Archive.org, like this one. You'll have to assess the validity of sources obtained this way.

If you haven't already, meet with a university librarian. Your university may have a librarian who specializes in history (so they may have a masters or PhD in history as well as a masters in library science). They know their collection, and more importantly, they may have helped another student doing this same topic a few years ago. I often get similar topics from one year to the next, and I often know which sources past students found most beneficial.

Your school likely has a research librarian who is there to help you, try to search them out.

If there is an emphasis on primary sources, you should reach out to archives which are open to the public. I'm assuming you're from Texas (based on your username) so I don't know how useful your local archives will be for this topic, but other archives may have digital collections they can point you towards. Start with big ones like the National Archives and the National Museum of the American Indian before moving towards smaller, more focused archives, such as this archive at the University of Idaho Library.

I would offer one observation and two pieces of advise. The set of sources you are talking about seem likely to not be published sources. Diaries and journals probably are not. Military reports might be in some government record system as might maps. It might be hard getting those because you will need to figure out what archive they are in, whether they have been digitized, etc. This might slow you down a bit.

I would advise that you try to find good secondary sources on the topic. Perhaps do a Jstor search to see who has written what articles on the Nez Perce war and the scour the footnotes to see what documents they have used and where they found them. Books would work equally well, but I sometimes find that short research articles can work better. Once you have the information on what archives house this stuff, then you can talk to your research librarian about getting access to it. Or for that matter, you can just ask them where they would grab stuff for the project beforehand.

I would also suggest expanding to other sources. Perhaps you might try looking through newspapers. A lot of universities will at least have an archive of the New York Times and they might also have access to the America's Historical Newspapers series. With that you can search to see who is mentioning the war and what they are arguing. Now, you want to do a military perspective so that might not be too helpful, but it might give you information on who the major players were (maybe someone wrote up a biography, maybe their memoirs were published, etc.) and there might even be quotes from individuals supposedly involved in the conflict.

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Hello there. Your question seems to be related to school work, so we just want to remind you, and any potential respondents, that our rules DO permit people to ask for help with their homework, so long as they are seeking clarification or resources, rather than the answer itself. This policy is further explained in this META Thread.

Additionally, while our users may be able to help you out here, we hope that you also will take the time to check out our six-part series, "Finding and Understanding Sources", which should hopefully prove to be helpful for you as you continue in your research.