Sorry to say I do not know who you can recomend. The consulting service you need would require some one to come in with a blower door and identifly all your leaks. them you need some one to come in and seal all the leaks and yet another to provide make up air for all the devices in the home that require air for either combustion and or venilation.
It is fore this reason that we sell less and less natural draft devices , instead of tring to solve the pressure balance problem a solutiuon is change oit the natural draft device with one that incorporates direct vent technology and does not require air for combustion from the interior of the structure, not the answer you want to hear, but more than likly the easliest solution