Pull one from a wrecking yard. I believe all of those W126 door locks were pretty much the same, so there are lots and lots of them around.

On a related note, I'd be very surprised if MB really discontinued that part. Perhaps they superseded it with a newer part number, but they usually don't discontinue a part completely like that. You can probably still get a door lock for a gullwing from the '50's so I'm sure you can get one for your car.

Get a free account at epc.startekinfo.com and look up the part number. See if it says "replaced by" and another part number.

They probably just discontinued the earlier model and superseded the part number of the late model part because it will fit your car. They don't want to carry 2 (or more) parts with limited sales for an older car, when one newer part will fit all of those cars.

__________________
'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)