If you are willing to, you can create a pokemon.com account, and set you preferences to receive newsletters. In the newsletter which comes on Oct 20, there is a special code that will give you access to the Pokemon Omega Ruby and Alpha Sapphire Demo.
You can create a Pokemon.com account anywhere you live, it is not limited to the USA. I live in India and am waiting for the newsletter.
To redeem the code once you receive it, do the following-
- Make sure your 3DS system is connected to the Internet, and open the Nintendo eShop
- Wait for the eShop to prepare
- On the top left there is an orange Menu button, tap it
- Select the second option that says Redeem Download Code
- Enter the Download Code and tap the OK button
- This should trigger the download of the demo if you entered the code correctly.
Hope this clears things up!