They were revised to get as much threaded length as possible. If you can't find them anywhere on the net you might pull them from a junkyard (1990+ M103)
Maybe an M104 uses the same?
If that doesn't pan out, I guess you could pay the MB dealer.

I would agree to using the longer bolts if you can, if your re-installing a cam (as opposed to one rocker set) take them down like a half turn at a time, rotating around all of them starting from the center ones and jumping back and forth to either side, opposite bolts, to the outermost pairs and back to the center again.

But, you probably already knew that.