Mine aren't for sale, but new ones, with new double stick can be bought through Shelby Perf. Parts for less than $100. I think they were $89 or something like that last time I looked.
Also, these are not aluminum plates, they are a composite material with the rivet heads attached. If someone has a used pair, they will most likely be destroyed or at minimum distorted by the time the double stick lets go.............
^^^^^Notice that the Black plates have natural aluminum color rivet heads, this is the way they come. The Shelby Mod Shop sprayed the earlier Black block-offs on the Super Snakes so that they had Black rivet heads if the block-offs were chosen and installed as an option instead of the upper side scoops.
This is also an item you may want, the interior plates..............
^^^^^If you don't also have these, the back side of the 1/4 window block-offs will be seen from the inside of the car and the multiple strips of double stick tape.........not a pretty thing to see from inside the car.
I agree with Robert. Just order a new set from SAI. I picked up a set of black block off plates used and when I received them I had to do a ton of work to make them presentable. The guy had used a regular screw driver and had messed the edges up pretty good on top of scratching them. In addition, I had to remove all the old double faced tape which was a chore. After I straightened them, reshot them and purchased a new roll of tape I would have been better off just buying new. On the interior I purchased the panels that match the headliner material. It turned out great. It looks factory. GL.