What do you mean by "popular cars"? If you want something specific maybe it would help to be more specific. Old cars? New cars? Foreign? Domestic (which market)?
There is a list of "AutoCAD block websites" here on the CAD Blog:
Did you already try CBEN? Otherwise you might try to Google the net for specific blocks one by one.
progeCAD support, tips and troubleshooting forum. progeCAD works very similar to some versions of AutoCAD. Moderated.