Seems hardtops were available in limited quantities in the UK (and I think there was a recent thread here from someone who had purchased one).
I've heard that you must remove all of the cab top parts to fit the hardtop. Here's a current example for sale. Its an '89 model -- I dont know what years they were made, or how hard they are to retrofit back to '83.
Porsche : Porsche 911 Supersport convertible with hardtop
