i shy away from watching things much longer than a typical episode from a website like youtube and such. you should look to see if you can order it from your local library, they have the special features, as they will prolly be in DVD form.
if you cant, then tool around online and see what comes up.
btw, heres my little review sans (that means without) spoilers
Advent Children-PWNS son! o own the special edition b4 everyone else (that i know of, purchased legally
spirits within- its ok, not as good as A.C.
unlimited- well, i heard bad stuff about this. never seen it.
hope i could help