Try:
www.rocklandstandardgear.com . They build transmissions of all levels, even offer different ratios if you desire to set the tranny up for a specific purpose.
Here is the link to the
Racing and Performance Area of their site.
The Viper racing tranny is model T56-018M.
List Price-$3500 Racer Net $2400, exchange
"Rockland Standard Gear produces race and performance transmissions for the top professional road race and drag strip teams, many kit car manufacturers, hot rods, and enthusiasts who wish to increase the performance and durability of their vehicles. We have bulletproof race ready transmissions for C5 Corvettes, Camaros, Firebirds, Mustangs, and Dodge Vipers, and rear differentials for the C5 Corvettes. We are the only ZF certified source for parts and transmissions for the ZF S6-40 6 speed transmission used in the C4 Corvettes from 1989 to 1996. Call our reman division at extension 130 and let our team of experts help you with your performance and racing needs. We are available to help you with your project."