The only turbocharged RX-8's out there are going to be custom jobs and even then they are most likely prototype pieces. There isn't a kit available yet (at least not on this side of the planet) and whether or not Mazda will release a turbo version is still the subject of heavy speculation. The only twin turbo rotaries out there are going to be RX-7's.
Greddy is also working on a turbo kit.
There are also a few companies working on supercharger kits.
We don't need 2 forums! This one works just fine. It's bigger anyways.