Go to your nearest dealer with your VIN and he should be able to print you a copy of the window sticker. Take in a USB memory stick and see if they will give you a copy of the WS in PDF form.
Ford Show Parts and if you are an member of the Mustang Club of American I believe the discount is 20%. You can also get a production certificate as well.
Tom
I got mine yesterday and laminated itI ordered a new one from ford performance, unfortunately mine got ripped in half at the dealership when they took it off.