Horn contact brush that goes behind the steering wheel

[Banick]

There doesn't seem to be any website that sells this part. - (Or if they do it is discontinued)

Part Number: 107-464-01-43

[David Robinson]

https://www.sl-repro.de/Hupenkontakte.html 

Don't know anything about this company.

[Leester]

I found an early r107 in a junk yard and the contact brush was the same as my 70 280SL. I suspect the W108 and maybe even 115 and 114 use the same contacts. Getting harder to find in junk yards but worth a shot if all else fails.

[Pawel66]

Yes, the part number is A 107 464 01 43.

And it is a good idea to enlarge scope of search to other models. Here I can help, here are the cars that used the same part:

107, 108, 109, 110, 111, 113, 114, 115.

For 107 - 20 sub types.
For 108 - 15 sub types.
For 109 - 9 sub types.
For 110 - 15
For 111 - 13
For 113 - 2
For 114 - 25 or so..
For 115 - similar

Maybe it will help.