Note: Harvard Business School cases are available online for a fee. The TUS Library does not provide access to these cases. However, each issue of Harvard Business Review contains one of the cases. Perhaps you'll get lucky. Harvard Business Review is available via Business Source Complete.
Case study abstracts and some full-text are available in the TUS Library subscription databases listed below. You can include "case study" as a keyword in your searches in these databases.
Also, some databases allow you to limit your search by selecting a "Document Type": case study.