I'm fairly sure they're dealer only parts. The corrugated pipe is 117 142 01 59, $30 list; the sleeve inside the corrugated pipe is 117 142 01 54, $21. Looks like 450SEL or SL part numbers if there's a wrecking yard near you. I'm sure Phil of Buy Parts -> FastLane can hook you up.

Sixto
87 300D