Ummm from an exhaust shop or a workshop.

I would talk to a workshop before running off to get your bits.

1. New dump pipe might not merge up to existing system
2. Might need some rewelding or modification to the exhaust system

There are most likely better mods to be done then just a splitter.

A splitter alone wont nett 1 zillion hp and 2 billion nm of torque. Once again, it comes down to application and your goals for your vehicle. In the 2.5in thread there's a graph of what a china bellmouth can do.. food for thought...