Amazon has numerous versions of gas can vent caps including some fancy metal ones.This is why I still use the gas can that I got handed down from my dad 20 years ago. The same one I used when I was a kid mowing lawns. In 30 more years it'll still be rocking it.
Where do you actually find these? My aforementioned gas can, it has a vent like this but that part may not last forever. It's started to have bits of it chip off from thirty-something years of UV exposure.