I expect that you CAN legally purchase R12 in Colorado as long as you have a 609 certificate. You can go online and take the OPEN BOOK test for $15. Then you can purchase R12 online or at your local auto parts. This is a national law, I expect that it applies in every state.
Where it IS illegal to purchase R12 is if you do not have the certificate.
It would be a violation of federal law for me or anyone to sell you R12 unless you have the 609 certificate.
BTW, the $15 is not a special deal for me. Auto Zone is selling it for this price (to 609 certificated people of course) if you can find a store that has it.