Hi,
The mirrors I have looked at with the dimming feature, they change the plug connections so a direct swap is,nt possible without cutting and crimping new different style crimps.
I believe the mirrors on certain year of SL's were the same as a 202 and prefacelift 210 so this may expand your options in getting a possible second hand mirror.
Have you tried ECP for a dimming mirror, I bought one from them at a considerable saving from MB, and with the forum discount it would be even cheaper.