Mike,
If you mean the NACA ducts, there are several places to buy them like Pegasus Racing, and Hoerr Racing Products. You can glue them onto fiberglass, carbon/epoxy/polyester using the flexible, waterproof Marine Goop.
Then it must be the twin nostrils. Contact [email protected] at Hough Composites since he carries all the molds for the GT-40 and may be willing to help with just that part.