A gentle reminder, list the year and model when you post an inquiry.
'Stormcloud', my 1979 W116 300SD (a model 116.120 in MB shorthand), has the same broken part as your 1979 W116 300SD.
I haven't been able to find the part number for you, but I did snag a replacement from the Newark Pick-n-Pull on the day I purchased 'Stormcloud'.
If I find another I'll pull it for you.
If you contact the
classic center in Irvine, CA with your VIN they can look up the part number and check availabilty worldwide.
The local dealership typically only checks stock in the US.