I take it, that it is the piece under the part SLS has numbered as "6". You may want to send them an e-mail and see if they have a source or option. Do you have the piece and need it recovered, or need the whole piece?
Perhaps, MB Classic, Millers, Neimoeller (aka the usual suspects) may have the piece. I just looked at Neimoller, and they show the part as available, go to Gruppe 68 on their web site and see if that is what you are looking for -
www.neimoeller.de. I was not able to get to the English translation, but it might be there, or at least a contact number.
Jonny B
1967 250SL Auto