Lost keys to 1988 VW Cabriolet.

I have a 1988 VW Cabriolet. I switched the ignition key with a spare lock with key that I had, but the set that has been lost fit the doors, trunk, and glove box. I would like to have a key (or keyS) made so I can re-install the original lock and maintain the ability to use one key for all locks. Where would I look for the code numbers to have new keys made? I appreciate your quick response. Vaughn in Rochester