Hey mate,
wereabouts did you see it? I live in good oul Norn Iron and have a 220d with twin exhausts? its a silver sport model, so it may have been mine you seen. To answer your question, JON exhausts in newry done it for me (www.jonexhausts.co.uk), excellent service and fairly priced. I have the SR bodykit for the 250 and the twin exhausts make the car look twice as good. most people say to me they wish Lexus had made it like it from the start.
i attached a pic above.