They have the Header colletor gasket for merly 7 bucks to go between the header and Cat.
I had to order a new one since I got pissed when doing an install and ripped it off the cat, because of a bolt striping and breaking off in the cat.. luckily I got the bolt out and replaced everything..
Go down to your local parts house and get some high temp gasket material with the metal sandwiched and make your own. That's what I've been doing and it works great. You can use a small ball peen hammer to tap it against the opening to make the outline before cutting. It cut's fine with a sissors and you can use a hole punch for the bolt holes.