Gary,
A car audio shop is a good place to find the raw materials you need for making a blank plate. I got a big piece of textured plastic from a car audio shop years ago and I've used it on several projects.
As for the carbon fiber look. If you want to save some bucks maybe you should consider making the blank plate out of plastic and then coat it with "Performance Carbon". This is basically sheet material of real carbon fiber that you just stick over the plastic. It should work great on a flat, interior project like this and it's relatively affordable stuff. The MachV stuff looks pretty good too. The Autometer plate is made for fitting under the dash and may not fill your hole properly.
Performance Carbon:
http://www.senkostyle.com/shop/home.php?cat=3