WorldCat, the world's largest library catalog!
The Van Wylen Library doesn't have every book or resource, it just isn't feasible! But, luckily for you, you can request materials from other libraries through WorldCat.
When you see a library item in your search results that looks like it might be useful, go ahead and click on it to see the record for the item. There you can look at its table of contents, its bibliographic information, AND, you can look at its Subject Headings.
Subject Headings are like "tags' that describe what the book/resource is about. You can use these "tags" as links to find other resources that have that same "tag."