get a belt sander and make sure the gasket surfaces are flat. then use copper rtv. never had a leak after this and i dont have gaskets anywhere in the exhaust system.
Making sure the surfaces are smooth and true a little copper rtv should do the trick
However if you are just wanting to have the gasket anyway, look for your closest SCE gasket dealer. If they dont have it they should be able to get it in a couple of days.
Keith, what you got were header collector gaskets. Although they can be made to work and look very similar there is a little bit of a difference in the outside shape and bolt hole locations.
I personally prefer to use the SCE one that is app specific.
Again though any of these options should get you what you need.