Just contact escorts, ask them if they're originally from Boston and if they could study the accent and use it with you for a "role play" session. Try talking to him on the phone to see if you like it.
You can also send them a video of "Ted" "The town" or "Good will hunting".
I don't know how often an accent is requested and not all of them might be able to do it in a convincing way, but it won't be the weirdest request they ever received.