There are two problems with this.
1. Scale models will not replicate the appropriate reynolds number if you scale the speed accordingly. You could either attempt to use a water tunnel to get a reynolds number that was close, and/or use trip wires the force the boundary layer to transition from laminar to turbulent at the correct location on the model.
2. In order to accurately model flow you'd also need to have a moving surface to place the car on, to account for the interaction between the moving car and the non-moving road surface.
As for models, maybe you could make your own wooden scale model like this:
http://www.woodenautomodels.com/
http://mahogonymodels.com/Cars.htm
I'll try and post some math about similar flow and Reynolds number later today . . .
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