I'm not sure where you can find that.  If you wanted a truck, sports car, or SUV then I might be able to find something.  When you want a specific make and model, then there is a good chance that it doesn't even exist.  One thing I might suggest, is make a list of all cars that look close to a supra.  If you can find a free file for a car from the list, you may be able to modify it to look like a supra.

After doing a quick google search, the closest I could find was:

http://www.3dxtras.com/3dxtras-free-3d-models-details.asp?prodid=9276

Is it even close to what you are looking for?

                  -David