Jemco in Houston makes custom exhausts. They built my expansion chambers for my Mach111 about 20 years ago. I talked to someone there about 4 years ago about a custom exhaust for a GSPD. If they build the exhaust you will need to leave the bikewith them. I was very pleased with their products.
Jemco Exhaust Systems
1919 B Blalock
Houston , Texas 77080
Where are you located in Houston? I'm by Reliant Stadium or Baja West University Area