Here are some suggested websites :
Arizona State University: Chicano Research Collection - https://www.asu.edu/lib/archives/chicano.htm
"The Chicano/a Research Collection is the largest Mexican-American archival collection in the state of Arizona. Established in 1970 in response to the academic needs of both Chicano students and faculty in higher education, we continue to serve students, faculty and the community and collect works by and about Mexican Americans, or Chicanos, in the United States." - ASU
National Association for Chicana & Chicano Studies - http://www.naccs.org/
"The National Association for Chicana and Chicano Studies is the academic organization that serves academic programs, departments and research centers that focus on issues pertaining to Mexican Americans, Chicana/os, and Latina/os." - NACCS
Library of Congress -www.loc.gov
Search for "Guide to Mexican American War"
National Archives - www.archives.gov
Search for " Military Resources: Mexican War, 1846-1848"