Well they made 20,302 69 Z/28's if you break those down by color percentages, I am sure you would be in thousands of silver cars still.
"Z/28 land" is a large country, "COPO land" is a small city, and "ZL-1 land" is a even smaller town.
"Z/28 land" is even harder to search because Z/28 land is always getting larger with all the clones. I would say the L.A. cars would be the hardest to pin point with no X codes as identifiers.
Try starting with the license plate if no paperwork exists, if that produces a VIN, then you can do an internet search.