Thanks for reaching out and for the suggestion!
Unfortunately, shortly after debuting the 'green key' system for it's propane canisters, Coleman stopped including them with the canister because many recycling facilities across the country were still unable to accept the canisters for recycling, even with the 'green key'. These 'green keys' are still available to purchase in some places, including some imitations. It sounds like you need to check with your local recycling facility to see if they are able to accept a propane canister emptied with the 'green key'.
Hopefully this helps, thanks!