The one I did as a student was a case that came in while I was hanging out with them one day. They knew I was hoping to find a case to present and the pathologists mentioned that it might be a cool one for me to do. I didn't just outright ask them to give me a case, but earlier in the summer I had mentioned I was interested if something cool came up that the residents didn't claim. Maybe
@WhtsThFrequency has other experience or ideas.