Aftermarket you have the choice of Amuse, Veilside and a GReddy I think, trying to find any of these will be difficult.
There is only one 3.5" exhaust on the UK market, TB Developments exhaust based on the Amuse R1 and it looks a nice bit of kit.
E2A
1st & 2nd 3.5' decat pipes with flex joint à la OEM here - http://www.mkivsupra.net/vbb/showthread.php?338434-TB-Developments-TT-Decat-Pipes
3.5" exhaust here - http://www.mkivsupra.net/vbb/showthread.php?331224-Tempted-to-make-my-own-range-of-exhausts
or contact GReddy US about their new exhaust here - http://www.mkivsupra.net/vbb/showthread.php?343956-NEW-GReddy-Exhaust-Prototyping