TimeVlave Manufacturing Company makes direct-fit OEM duplicate catalytic converters. They have advertised in The Star Magazine forever, and have a great reputation.
In the March / April 2003 issue of the Star Magazine (which just arrived in the mail today), there is an advertiser that I haven't noticed before, but I'll post it here anyway and let you call them:
Borla East - Stainless Steel exhaust systems for Mercedes Benz Cars, standard steel exhaust systems, replacement catalytic converters, etc.
908 - 236-2820
24 Cokesbury Rd., Suite 9
Lebanon, NJ 08833