Hi.
I had the same problem. The "cheesy" orange stock gasket just crumbled-up and fell apart.
Someone on this forum recommended cutting my own with EGR valve gasket material from an auto parts store.
I had problems finding it (EGR gasket), but the tech at an O'Reilys looked-up the temp specs on a "Mr. Gasket" acrylic (about 1/8" - 3/16" thick) product (rated for 2-cycle exhaust manifolds), and recommended it. The sheet costs about $8 (US). The material is very tough and "leathery". I had to use my Dremmel to cut it.
OReily's had a lot of good prices on small engine parts too (like inline fuel filters, manual choke cable, etc..).
I've been using the same gasket, even with two different mufflers, and it still holds and seals great. I highly recommend it.
VaporKing
150 Miles/Gallon
"If it doesn't kill me, it makes me stronger".