The chances of finding the original one is 0 and none. Whoever took the dash panel needed it for some sort of repair or they would have taken all the other items with the VIN on it (not likely on a slant 6 car). They would have removed and thrown away your VIN plate and installed theirs to complete the swap. You can go to the Ca. Highway Patrol and have them assign a new VIN plate for ownership and registration purposes. They usually use the original number if you have good paperwork.