OEM is available on Pelican:
Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

If you want stainless, you can check Timevalve's pricing.
Mercedes 1970-72 280SE 4.5, 300SE 4.5, 280SEL 4.5 and 300SEL 4.5 Exhaust System