Most any autoparts store sells the Auto Ventshade brand (they are shrink-wrapped on yellow backed cardboard), and any labeled for the Explorer or Explorer Sport Trac will work. That will cover the side windows. Get the in-channel version and follow the instructions exactly to install.
As for the rear, I bought mine from www.fordpartsfast.com, click on the specials, scroll down, it's $49.95 + $9.95 shipping.
P.S. They work excellent. First mod I did for my 04.
TJR