there are classified here, or "parts for sale" sections, also b15u.com seems to be the most active for classifieds, the closer you are to ny, the faster youll get your stuff.
if youre capable on removing and reinstalling the header, all you need to do is use a long screw driver or something and smash out the cermic plates. dont get dust in your eyes, it will hurt like hell. hopefully you dont live in a smog state, if you do you shouldnt ruin your stock header. also, dont forget about some antifoulers so you can foul out your lower o2 when you gut the precat.