Some textbooks include case studies on related topics. Some of these textbooks include the word 'cases' in their titles. A useful tip is to try including the word 'cases' in any title search you carry out. e.g. finance cases.
When searching Library Search, remember to filter by electronic book.
You can search on Harvard Business Review for case studies. Use Library Search to find Harvard Business Review.
You can find case studies on Financial Times. Use the quick search to search for case studies and then select the result which is in the News section. (This page contains a link to the Financial Times.)