There are some aftermarket race specific manufacturers. I don't have my list with me here at work but I'm sure if you do an internet search you will find them. There are also some places with just the tubing to make your own system. The problem with titanium besides expense is that you have to weld it in an argon gas filled chamber. However the strength, weight and non-corrosive advantages my outweigh the hassle.
BTW Arvin Industries is the OEM sub contractor for the Z06 exhaust.