My worthless two cents...
A 'trim tag' or 'buck tag' is simply a plate attached to the body denoting its options, colors and where it was built. It is NOT a VIN. Since its missing, and what the others have mentioned, for a 'correct' car it will be a slight loss in value. IF you intend to build a modified car, its not really needed anyways. However, ANY potential car worth owning should have one in place. I'm not qualified to comment on a Camaro's reproduction buck tag, or where you can have one made. I do know that in the Ford world Kevin Marti will sell you one for your car...IF you can prove you own it.