Chainsaw Repair

I have a Dolmar 112 I made those same gaskets for.
I went on eBay and bought some fuel resistant gasket material.
I also used a leather punch for the holes.   Like you said the impulse goes through there and a leather punch has a variety of hole sizes.   I have also used a single hole paper punch if a hole that large is needed.
The rest of it I cut out with a razor blade on top of a piece of cardboard.
Take your time and you can make a good looking gasket when done.