It is a regular 4pin connector. You have all the parts numbers here:
https://www.sl113.org/wiki/Electrical/ConnectorsI am not sure about availability, you would just have to order the parts with the dealer to check potential substitutions.
Particularly for fuel sender the history is:
A 000 545 32 28 up to chassis 113042 012466
A 015 545 49 28 as of chassis 113042 0 12467
and then there were series of replacement numbers.
One important point: if you had the fuel level sender with float and lever and you replace it with tube type fuel sender, it will not work unless you also replace the gauge in the dash board instruments.