Howdy,
I don't know about auto supply stores but many HD dealers and indi dealers carry many brands of replacement exhaust gaskets. Cometics is allegedly the best and some say James. The stock and SE gaskets can sometimes interfere with the exhaust flow if you don't get them seated just so. A trick some use is to make the solid type a little oblong by squeezing so that they stick in the head to make it easier to install the header pipe.
Best,
Pixs :cheers:cheers:cheers:cheers:cheers