Ventura County is notoriously lacking space for this type of event. There's a couple of alternatives if you're willing to go a little further South. The Paramount Ranch (I think it's in Hollywood) may be able to accommodate that many cars. You might also want to check out Willow Springs, but in July/August, you're talking about a really HOT day at the track.
The Dallas Convention Center or the Traders Village in Grand Prairie are exceptional places to accomodate the kind of event you have in mind.
Special Events Planner
Pioneer Event Center
If San Diego is an option, you should check out VisionPulse Creative Events. We recently hosted a car show. You can reach us at 858-605-6262 or 619-549-0398 ask for Elisa or Ed
September 2, 2010
Franklin Mills in Philadelphia has car shows in their parking lot. I'm sure other malls would work as well.
Huntington Beach Pier has a lot of car shows - not sure the size you're looking for, but they attract a lot of walking traffic for such events. No indoor, but bathroom facilities are available.