I have been looking for this too. there was a post previously but the pics are gone
http://www.lexusownersclub.co.uk/forum/topic/51758-custom-make-exhaust-on-is220d/
found this on google
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSFJCpoNr52SLFmelHhfFlOWwnMqVyV-tlap9HxLFHvQbMecOKA
https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcR2nBCKSqhqO2V1k75nWhLdKPkqNlIaKDHh2DLr6JoE93haeBTf
think the only way to go for me is a custom powerflow exhaust or backbox. havent found many decent garages around n.ireland :(
