The build sheet was attached to the top of the gas tank. Sometimes extra copies were left it the seat springs, under the carpet, or up under the dash. The line worker just stuck their copy there rather than finding a trash can.
If you '81 was built at Bowling Green you can get a copy from the National Corvette Museum. Bowling Green cars for '81 had a "5" in the 11th place in the VIN. St Louis cars had an "S".
Tom has all the right answers including the Bowling Green option. If you have a "5" in that fifth slot in the VIn then your troubles are over. The NCM can get you (for a nominal fee) not only the Build Sheet but the Window Sticker as well. However...... if you are a St. Louis guy like me, then finding the Build Sheet(s) in your car is your only hope. Good Luck and welcome to the Corvette Action Center.
drsantos ~ Welcome to the Corvette Action Center Community ~
Ditto and what has been said, with one exception. On the drivers sided door frame by the dash you will see a little rectangular aluminum tag with numbers and letters on it. This is the "Trim Tag" and will give you the color and interior options. You can go to the Model Center tab at the top of the page and enter 1981 to see what factory color and interior you should have. Or I invite you to the L81VetteRegistry and check out the specs pages there too