Hi Stephen, I assume you want to revert to original? There must be a number of owners that have swapped the other way around. Perhaps if you don't get any mirror offers here, try starting a thread in the Wanted section of the Forum.
Regarding the suitability of fitting - I stand to be corrected but I believe the SC, Carrera 3.2 and 'Flag' type on 964s mirrors should fit. The non 911 'Flags' (924/944 etc.) have a different stem as its foot has to fit a different radius of door skin. When I have seen door mirrors offered I have only seen the mirror complete with the stem section attached.
Perhaps someone that has done this swap either way can confirm if the Flag mirror can be transferred on to the teardrop stem, this would make your quest easier.
Steve