Welcome to FTE. In future posts, be sure to include the fact that you have a 6.0 motor since several engines were available in 2003.

To answer you're question, we really need to figure out what he is calling the Y pipe. Did he show you or describe what the problem is? The Turbo has a Y shaped collector on the back of it that your bellowed up pipes connect to. Those will be dealer items, or if you don't mention it's for a Ford, you can also get them from an International dealer. Those 2 parts are not something that usually go bad, even with neglect, so I'm curious as to what happened to yours.