stuff hunting around town for a month of sundays for gaskets, just head to the auto parts store and buy a sheet of blank gasket sheet, they should have a few different types of material like cork,paper etc etc etc, in all kinds of thickness. mark out the outline, and cut it out. wallah, bobs your uncle.
i made some for the fuel bowls on my carbys(hitachi su's) and they came out like bought ones.
i have some spares if anyone has been hunting for some.

if worst comes to worse, just cut out a cornflakes box.