Check here for some production numbers.
Here are some FAQ things:
For most things you will be able to us any OEM Part for the 240sx from 91-94, no matter if it is Convertible, Coupe, or Hatchback.
There are no OEM parts available new for the convertible specific parts (just as tops, rear windows, etc, etc). So used (ebay, on here, etc are the ways to find those parts).
If you give specific parts you need I or someone else should be able to direct you. A few online Nissan dealers would be a good place for searching for OEM parts.