Harvard Business Publishing makes a great deal of money selling these for business school course packs and will not make them available to libraries. You can, however, order them directly from HBS, around $8.95 each
How to find them:
Use keyword searches in article databases . For example: "case studies and airlines" or "case studies and management". Full-text articles and abstracts are available, depending on the journal.
Tip: Use the subject heading "case studies" in ABI/INFORM and Business Source Complete
The Case Centre has case studies available from many major international business schools.
Darden School of Business at the University of Virginia has searchable collection of case studies online. Abstracts and video previews are available but you must purchase any studies that you want. Verified faculty have free access to all content on the site.
Stanford case studies are searchable online. Many of these are available for purchase through Harvard Business School Publishing or the Case Centre.
Harvard also sells cases from Babson College and Northwestern's Kellogg School of Management, among others.