The OBX catback still seems to be available from this vendor for $279 :
OBX Cat-Back Exhaust 2004-2006 Chrysler Crossfire 3.2L 04-06

I have had one installed for a year and a half now, just a bit of drone in the 60 - 75 range, but overall a smooth mellow sound.

( This a Chinese rip-off of the $800 Borla system, identical in every way including SS grade )