Automotive Data Sources

Hey everyone, I am trying to find a source of information that will tell me sales volume of specific automotive manufacturers by state. The only websites that I have found as of right now that might be able to give me this information is Ward's Auto and Polk, but so far, I have been unable to find the data I need on these sites. Does anyone know of any other sources where I could find this data? I am not familiar with doing this kind of research so forgive me if I overlooked something blatantly obvious :cool:.