like stated before, trunk lid and hood are that composite stuff, all of the other panels are metal aside from things like rocker panels and other "add-on" bits.
The 4th gen f-body's panels are all composite and it still weighs more than the mustang.
Check out both of these places. I bought a front bumper from the first link, and I have heard good things about the guys from the second link. You need to call them both though, don't rely on the website to order.