I just replaced the entire exhaust on my car. The front pipe and center muffler seem to be all but unavailable in the US. I managed to get the last front pipe from the Bosal warehouse, and I found an unused Bosal center at a local parts dealer. I also bought a complete used OEM system in case I need a spare at some point. There are at least two variations on the exhaust for the OM603, and the parts are incompatible. I've posted a page summarizing the differences:
MBexh
MBexh