I do this kind of research a lot, too, and I typically have very little luck with the internet, even websites that I only have access to through my school.
Have you looked in your library’s section of textbooks? Also, have you checked the downtown branch, not just your local branch?
You may not be able to find a book that deal solely with Nicaragua, or solely with the church, but maybe you can find several Latin American history books that you can cull information from. You’re definitely going to want to look into interlibrary loan, as well. Just because they don’t have the books you need now, doesn’t mean they can’t get them.
Here are two books that look perfect for you:
Michel Gobat, Confronting the American Dream: Nicaragua under U.S. Imperial Rule
It’s about “National State and Society from 1830s to 1920s”
Justin Wolfe—Those That Live by the Work of Their Hands: Labour, Ethnicity and Nation-State Formation in Nicaragua, 1850–1900
Here is a long list of Latin American history texts focusing on different subjects.
If I was in your shoes, I would google for something like “Nicaragua Course Syllabus”, “Religion Latin America Course Syllabus”, and “Latin American History Neocolonioalism Course Syllabus”, find the names of books profs are assigning about the topic, then go to amazon.com, and search for the ones that look helpful. After you’ve determined which ones you really want to look at, search for them on your library website, and if they don’t have them, request them through interlibrary loan.
Best of luck! Feel free to PM me if you need addition help!