It is easy to make your own gasket. I got a small roll of paper gasket material (light brown in color). from O'Reilly Auto Parts but bet others have it. You can cut it with HD finger nail sissors to allow cutting the curves. Then sharpen a small piece of metal tubing to punch the holes. You can trace the pattern from the top casting and the bottom casting on HD paper, cut and transfer to gasket material, mark and cut.
Hope this helps