Harvard Business Case Studies are published as textbooks. There are cases in the Harvard Business Review, but they are not as complete as the type that must be purchased. Free cases may be found in the databases, and of course, they vary in quality. Below are a few slides showing you how to find these cases.
You can see below that there are several ways to limit your search on Cabell's. Click the MORE button to limit by Difficulty of Acceptance, etc.