Check the California Air Resources Board Aftermarket Catalytic Converter Database at ssl.arb.ca.gov/PartsSearchTool/CatalystSearchTool.aspx. It appears AirTek, Inc. and Car Sound Exhaust System, Inc. make aftermarket CATs for your ZR-1, however you may very well be correct and these particular catalytic converters not fit your non-base model Corvette.
If you feel you've exhausted all efforts in finding a CARB approved aftermarket catalytic converter for you car, feel free to contact the California Parts Locator. The Parts Locator service might be able to help you find the CATs.
If they are unable to find you the part, they may be able to issue you a "Limited Parts Exemption". You may contact the State Smog Check Parts locator by calling 800–622–7733.