Now a days, probably a yard sale. Most new cans have the integrated venting system for "safety". Maybe on-line, like ebay or craigs list.
All you need is a spout with an air vent in it. Or buy a can with such a spout.
They should be available almost anywhere.
Plastic can? I just poked a small hole at the very top of the can furthest away from the pour spout. I insert a small plug to seal the hole when I'm not pouring gas. Black plastic plugs from the irrigation section of my hardware store. Just don't overfill the gas can.
ebay is recommened, and maxspeedingrods is also a nice choice, some item in maxspeedingrods are cheaper than ebay store.
Ace is the place with the helpful hardware man.
car quest auto parts
Is there a place on line that sells a real gas can? One that has the air vent in it so that it doesn't take 5 minutes to fill my mower.