This is kinda weird but how can I find a hospital with a dedicated diagnostics unit?

Your best bet would be to try to find one at a large teaching hospital, such as university of maryland, or johns hopkins. However, it sounds like you are far from even thinking about that--so concentrate on the education first--who knows what medicine will be like by the time you finish (in 6-10 years +). Medicine is in a pretty big state of flux, and things can be quite different for the future. There is also research type diagnostic positions as well, including CDC etc. Good luck.