Hardware such as nuts and bolts, that was not proprietary, has all but been eliminated from the MB parts list.
Take a photo of the bolt or get the measurements, and go to Fastenal, Brafasco, Grainger, or any number of other local fastener supply houses and you'll be able to get what you need.
It is this specific ease of finding metric hardware why MB discontinued these items.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored