I'm sorry I missed your PM (I don't check in here very often anymore).
We contacted a local car club to get the names of some owners who rent out their cars for parades, events, etc. My husband took care of this, so I don't have the name or number of the person we used on hand, but I would think you should be able to find car clubs in your area via google pretty easily. If you're really looking for a specific name, I can find out that info and get back to you. It was significantly more affordable than going through a rental company.
A word of caution/something we learned along the way... some owners will not commit to a date until as late as 3 or 4 days before the event to make sure that the weather is clear. The first car we had booked ended up canceling on us 4 days before the wedding because there was a chance of rain in the forecast (it poured the day before, but our wedding day was about as beautiful as they come in September). We were able to find someone else at the last minute, so it all worked out, but it is the drawback to going that route versus a rental place.