The white seat in your picture is a 1973 or 74. I'm not sure if they are available in reproduction, you'll be stuck looking for used.
The other red parts shown in the first pictures are not Mopar parts that I'm aware of.
The rear seat frames are slightly different between Cuda and Challenger. They will fit each other, but won't look correct. That is true for 70-71, not sure about the later ones.