Where do I find these gaskets to seal around my exhaust? 6" x 4" inner diameter

http://www.cpperformance.com/c-467-transom-rings.aspx

I made mine....One stop at Auto Zone and pick up some "fell Pro or Mr. Gasket, or any other sheets of gasket material and cut them yourself and I used Clear silicon....set me back a solid $10 and I have plenty left over..... Works just fine

Thanks Griff, I can never find anything on websites.
$20 a gasket is a little extreme.

I will be going the Autozone or Mcmaster Carr route. That is what I planned on doing if I couldn't find any. (reasonbly priced)

find a locall rubber place , its just some kind of neopreame rubber.might find some that will hold out to some heat, the ones I got from stelling ya could cut with a box cutter.