Hey. While I read a lot, I am not that knowledgeable in this area but it sounds like the OP is looking for somewhere to get brain imaging tests (fMRI, PET, etc) that they think will help in dx. While research studies use these imaging tools, from what I have read they do not seem to be all that useful in diagnostics or actually differentiating among similar mental disorders (depression, bp, schiz).
I would also imagine that they are very expensive, and even if one were willing to pay out of pocket you would probably still need a prescription for such tests from a doctor. I would think any major imaging lab or research hospital would probably perform such tests?

That said, if this is important to you, why not look into current clinical trials going on that would use these scans as part of their research? Check out https://clinicaltrials.gov
Best of luck.