Usually what i do in cases like these, is to to take a trace of the CAN bus on a working vehicle and then replay this data to the DUT selecting and deselecting

Usually what i do in cases like these, is to to take a trace of the CAN bus on a working vehicle and then replay this data to the DUT selecting and deselecting different IDs, then i apply random values to different bytes of the responding IDs and observe the reaction. It can be time consuming but more productive that trying to contact OEMs. Also DBC files can be of some help.