Lexus still sell original accessories for the IS200/300, i just purchased a boot liner and a set of mudflaps.
These 3 sellers on Ebay are all Lexus main dealers, could do you a good deal...
2008holdcroft
inch63toyota
lexusbirm
Lexus do not make them anymore. Maybe a dealer may have some but you will have to get them to do a search of all the dealerships to see if any of them have a set. I got a set about a year ago by getting them to do a search. Got mines from Ipswich.