Most farm supply stores sell filler replacement pieces for gas cans that have no flow restriction devices. I know Atwoods and Tractor Supply have them.
You can thank a lawyer for the requirement on your gas can - someone sued the 1990's gas can maker and won millions for a stupid error - but the jury agreed with the guy that got burned because gas spilled out before he got it into the gas tank and the muffler caused it to explode in his face. They went out of business and a gas can went from under $5.00 to around $20.00 because of that lawsuit. More of the gas can is to pay for insurance for the manufacturer.
You can thank a lawyer for the requirement on your gas can - someone sued the 1990's gas can maker and won millions for a stupid error - but the jury agreed with the guy that got burned because gas spilled out before he got it into the gas tank and the muffler caused it to explode in his face. They went out of business and a gas can went from under $5.00 to around $20.00 because of that lawsuit. More of the gas can is to pay for insurance for the manufacturer.