I have not tried to make my own so far but I would make sure to select a material that was either 100% natural fibers or confirm that the other materials are compatible with gasoline. From the few samples I looked at they all seemed to be useful with grease and oil.
I orderd this one. It will be awhile until I get done with this project but if it works we should have an answer to this question for future saw restorations. You can buy these bigger so maybe you can get multiple filters from it at a much cheaper cost.