Four rotor engines are very rare and most of them were for race cars only. You might find one in Australia. I heard rumors of some being for sale there.
Now three rotor engines can be found at many JDM dealers. They were found in Cosmos cars sold in Japan.
There is a way to make a four rotor engine, but it requires a custom crank shaft.
Try the RX7 or RX8 forums for more on places to get the crankshaft.
