I need to have my mothers body exhumed for a second autopsy. In order for the surviving family closure this process needs to happen. Who do I consult with?

This question will generally have a state specific answer as body exhumation is regulated at the state level. This means that the answer provided here will be general in nature and may not address the specifics of the requirements of the state at issue. That being said, exhumations generally require either a court order or the consent of the next of kin. Court ordered exhumations are generally only necessary when the person requesting the exhumation is not the next of kin, though some states narrow this further and require a court order unless the requester is an heir to the person being exhumed. Based on your question it sounds like you would be considered an heir, so that should make it easier.
An heir will need to get a signed affidavit affirming their status as heir. This can be provided to the cemetery to allow for the exhumation. In some states you'll also need to have the approval of other next of kin, while in others it is sufficient to merely notify the other next of kin. Either way, you'll need to consult with any direct relatives of the person being exhumed. Various companies do offer these services and will likely have more state specific information available about what they need to be provided before they can exhume a body.