Many of those saw did not use a gasket, the or steel aluminum body of the "muffler" just clamped directly to the cylinder.
That said, gaskets were used on other models (PM6, 300 Ser) that match the mufflers on the Mini Mac saws, 68747, 83948, and 84992 are all examples of gaskets that will work.
I have some 83948 available for $1.95 + shipping if you are interested.
Mark
P.S. The Mini Mac 6 is the most difficult saw to work on since the starter is not removeable, to extract the engine from the housing you have to align the starter "ratchet" with the fins on the flywheel as you move it past. If you pass the test on a MM6 you will find the other models much easier to work on...