You have to buy the whole kit, I have looked into this myself. I think Hooker sells a tail pipe kit, but it goes straight out the back like a MC SS, not out the sides like a GN.
You could check with venders like Mark at trcustoms, GN1 performance, Cottons performance or Full throttle to see if they have some take offs.
Some of the cars they work on may have changed directions.
It's worth a shot.