There's a couple options for upgrading your stock throttle body.

Mantapart.com would be the first option. They can get 56mm throttle bodies for 2.8's, 3.1's, 3100's, and possibly the 2.0's and 2.2's as well. You can find pricing and more info on the website. http://www.mantapart.com/engines.html - Start at this address and click on your engine for more info and other parts available.

RS Motorsport is another option. They have 57mm throttle bodies for 2.8's, and 3.1's You can find pricing and more info on the website.