You would have to likely contact the makers of the reproduction panels or one of the vendors that carries them, not AMK since they are basically hardware. Believe these are attached to the repo quarters being sold but don't recall them being available by themselves. Someone like NPD should be able to answer your question quickly though you may be left with looking for one from a donor car or replaced quarter panel.
When you find out, post here to help others who will read this in the future