For old broken down cars you might try ghost towns, if there are any in your area. For example, the Bodie State Park in California has old cars displayed just as they were sitting when everybody left the town of Bodie, it's near the Nevada border, east of the Sierra Nevada Mountain range, in California... For nice well kept cars and taking photos with models, I would look for car shows in diners, malt shops, etc., they are all over the country, especially in the summer, a lot of times each week or month at the same place. The backdrop of a 50's diner or malt shop might make a nice period photograph, especially with a sepia lens filter !

You might check cars shows in the area. The oldride events has a real good list.