A number of years ago, Hasbro began the "Alternators" line of figures with the Rally Spec WRX which was sold in stores in Australia. The Alternators consist entirely of real cars including the Mustang, Rx-8 and DC5-type R to name a few. There are still a few Alternators left in Australian stores, but most commonly in Toyworld or specialty stores. If you find one, you're fairly lucky. Alternators retailed at $50 a piece, but can generally be found lower back in the day.
In Japan, the Alternators are known as "BinalTechs" by Hasbro's partner company, Takara. They are exact replicas of the Alternators, except they contain diecast parts. Expect to pay double the price for these. $80-100 a piece is what you should be paying delivered to your door.
As for where to buy them, online is your best bet. Try stores that specialize in Transformers figures and of course, eBay.
Personally I only buy, and have a number BinalTechs; as they were far more limited and will hold/gain value better than the Alternators.