The v6 can use the passenger side axle-back from any of the GT kits. If you convert your car to dual exhaust you should be able to use any GT axle-back kit.
As for cat-back there are plenty of kits out there by Pypes, JBA and Magnaflow as well as others. You shouldn't expect to see a performance difference between a hi-flow single muffler and a dual exhaust setup though.
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