Dr. Mariana Castells at Brigham and Women's in Boston is one of the top MCAD experts in the country, and anecdotally speaking, I know of several POTS patients who have gone to see her for their MCAD so she likely has at least a peripheral knowledge of POTS. I would say your best bet is probably to try to get in to see Dr. Castells for the MCAD and then ask her who she recommends you see for POTS. Truth be told, I think we've batted the subject around here on the forum before and haven't come up with the name of a good POTS expert in that area that anyone knows of, but you may have luck with the "in" of going through Dr. Castells first. (I could be recalling incorrectly, though, so if any of our community members in Mass. knows of a doc in that area, PLEASE do correct me!)
Other than that, the usual advice applies: head for the largest teaching hospital you can find and look for an electrophysiologist-cardiologist or neurologist who has experience/knowledge re: POTS/dysauto. You can usually cold call secretaries at their offices and ask if they have any expertise in this area and they will ask the docs and call you back within a day or two to let you know if you'll fit in well at their practice.
One other option is to go to one of the hospitals in NYC that has a fully-outfitted dysautonomia clinic. If I recall correctly from talking to my best friends in college who were from Boston and NYC, respectively, you can easily get back and forth between the two cities by train. You may find that to be a good option for you if you want to be seen at one of the top dysautonomia centers in the country. Here's the contact information for those:
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Specialists/show/717?cid=196