Textbooks are probably the largest source of case studies. However, they can be difficult to find in the Library Catalog. Try the suggested keywords to locate case studies as well as use keywords on your topic and popular textbook publisher names (McGraw Hill, Prentice, Thompson, etc.).
Another strategy for finding textbooks is to locate the call number range of your subject area and browse the collection. Textbooks often can be distinguished by their cover (hardcover), size (generally larger than popular reading titles) and title (often include words such as principles, practices, applications or have generic sounding titles such as Contemporary Marketing, International Business: Text and Cases, Negotiation: Readings and Exercises, etc.).