Nintendo Australia currently has a promotion where you can get this Nintendo classic by registering/linking your Nintendo Network ID (used to access apps like miiverse). The codes will be sent to your email starting on the 13th February 2014.
THE PROMOTION IS NOT ASKING TO REGISTER ANY CLUB NINTENDO CODES
Here's a copy and paste of the relevant section:
Join
Nintendo Network Promotion: Following the 10th December system update, Nintendo 3DS owners who have registered a Nintendo Network ID on their system, or have linked an ID they currently use on their Wii U console, can get a free download code for Game Boy Color classic Super Mario Bros. Deluxe on Nintendo 3DS Virtual Console if they perform this registration process between 10th December 2013 and 31st January 2014. Download codes will be sent between 13th February and 28th February 2014 to the email address registered to an owner’s Nintendo Network ID.
so what do u do specificly ?