I swapped the entire seat. Back in the 70's I didn't care about originality!
There are lots of power bucket seats out there that could probably work. If I were you, I'd take measurements of what I currently have and then go down to the wrecking yards and see what they have. You should be able to find something that will fit, even if it's just the mechanics.
I don't know about aftermarket. I haven't heard of anything.