Anyone who sells a 4.2 engine..Brison, Fox, J&A, Air Hobbies, etc..Same cylinder...
Easy enough to make one..You can get a small piece of gasket paper from an auto supply store...Nothing special about the gasket....Take the gasket paper, lay it on the bottom of the cylinder, gently tap around the bore and outside of the base with a small ball pein hammer..Takes about 2 minutes...