A contract is a contract right? Break it and pay the fines?
1) We make a Non-profit organization, name it 'Responsible Airsoft Canada' or something.
2) Get a contract made up between the buyer of said airsoft purchase and 'Responsible Airsoft Canada'
3) Within the contract state that the buyer will not break any laws, or let any minors use the firearm.
4) place a monetary value that is payable if the contract is broken.
Compaign the 'Responsible Airsoft Canada' name to Canadian retailers. Certified retailers make all buyers sign the contract. Give them an image to display on their websites.
It would place the blame on the parents if anything bad did happen and names were released. It also might make them think "I'll have to pay XX$ if johnny does something stupid with it?"
Far stretch? Yup.