I'm currently speaking to one of my manufacturers as we speak about this. I think carbon would be too expensive but GRP would be possible.
Here are a GRP and carbon one I've had made for the Evo 5/6 by the same manufacturer:
http://www.carbongoodies.co.uk/Evo-5-6-Carbon-Fibre-Rear-Diffuser-To-Fit-Standard-Bumper
http://www.carbongoodies.co.uk/Evo-5-6-GRP-Rear-Diffuser-To-Fit-Standard-Rear-Bumper