Go to a CNC machining shop with CAD Capabilities. They can make any type of knob you want. No use in asking questions in this thread lol since the only two people with information are 99% over at V6peformance.net and not this site...
All you need to do is take your knob over to a CNC / CAD Capable shop and they will measure it, turn into a CAD file, input it, and there you go... a knob
I would find the RX-8 ones because I'm sure custom 2 knobs would run at least 50 bucks.
If you want to go a cheaper route. Take it to your local Technology school and get some students to mill them out of metal. That's what I would do if I needed custom metal