There are 15 VATS codes.
You can try and take proof of ownership to a GM dealer and see if the the key info is on file. I can tell you it's definitely hit or miss with records this old, but maybe you'll get lucky.
If that doesn't work you can try to see if the dealer or a local locksmith has a VATS Interrogator.
Lastly you can install a new ignition lock cylinder. The new cylinder comes with a generic key with no VATS pellet, but it will at least allow you to turn the ignition.