When I was in nursing school, we were simply given the case study- A short synopsis about the patient with pertinent assessment data, lab results, MAR, etc. Then we had a list of questions to answer about the case study. The case studies were either written by the teacher or (more commonly) taken from an online resource database that the instructor had access to.
As students, we weren't given any additional information, but were expected to use our available resources (text books, internet) in order to answer the questions. Also, case studies were given as part of our lecture/theory classes, not clinicals. Our clinical instructors were responsible for grading our care plans each week and overseeing our clinical practice. They did not give any work unrelated to the patients we were assigned each week.
If you're a clinical instructor, you should get a copy of the textbook that's used for your students' theory class. There should be lots of case studies in it, and often there's a disk with it or a website you can use with it. You can use those things.
I usually make up my own case studies for my students (and use them in both clinicals and theory), and base them on things we're talking about at the moment, or things they've seen in clinicals.