The official Nintendo website announced further details on how to obtain a demo code for Pokémon Omega Ruby and Pokémon Alpha Sapphire in the United States. The details below are from their press release. Our ORAS demo page has been updated with the latest dates and locations to get codes.

Pokémon Omega Ruby and Pokémon Alpha Sapphire Special Demo Version

The Pokémon Omega Ruby and Pokémon Alpha Sapphire games will arrive on Nov. 21, but you can get a taste of them early with the Special Demo Version.

This free demo lets you experience exclusive scenarios in the Hoenn region. You’ll encounter Pokémon that will Mega-Evolve for the first time—and you’ll even be able to bring a new Mega-Evolved Pokémon into the full version of Pokémon Omega Ruby or Pokémon Alpha Sapphire. Items that you obtain while playing can also be transferred to the full versions once purchased.

How to get a demo code:

• Codes will be distributed at select cinema locations nationwide from Nov. 7–Nov. 13 (while supplies last).
• Check with your local retailer during the holidays to find out about special demo code giveaways (while supplies last).
• Get a code with your purchase of the new Pokémon Art Academy game (out Oct. 24) when you buy from Nintendo eShop on your Nintendo 3DS or 2DS system.
• You’ll also get a code with your purchase of one of two classic Pokémon games coming to the Virtual Console service on Nintendo eShop: the Pokémon Puzzle Challenge game (out Nov. 6) or the Pokémon Trading Card Game (out Nov. 13). You'll find your free demo code on your eShop receipt (download codes available while supplies last).
• Codes will be emailed the week of Oct. 31 to select Nintendo customers with Nintendo Network IDs who have signed up to receive promotional emails from Nintendo.
• Codes will also be distributed during the holiday mall tour from Nov. 24‒Dec. 21 at 16 different locations throughout the nation. Talk to a staff member to try out Pokémon Omega Ruby, Pokémon Alpha Sapphire or any of the featured Nintendo 3DS games to receive two codes—one for you, and one for a friend (while supplies last). Check back soon for a list of tour locations.

Source: http://www.nintendo.com/whatsnew/detail/q-_odTxvSXW6AVesSiQazTQhq2lKENNc