There are different types of AIS units. For some of these units you can determine the vendor and sometimes the unit code.
The vendor list for AIS-SART, AIS-MOB and EPIRB can be found on the CIRM website by using this link http://www.cirm.org/services/ais-sart.html
The vendor list used in msg 24 part B of AIS available on the NMEA website. You can go to the NMEA website by following this link http://www.nmea.org/content/nmea_standards/manufacturers_c.asp The unit codes are not available at the moment.
The availablity of a vendor-id in the lists will not garantee that the units may be used yet. This is determined by ITU, IMO and in some parts by local legislation. Using units that are not certified for their purpose and permitted by legislation could result in a penalty by using them or by detection by an official body.