go here for the full version , and here if you want the trial version.
follow instructions on there and you'll have to sign into the site with the email and password associated with your xbox live account.
and for future use for any other songs, you can find the links for any other songs before they hit the stores with www.rbnreleases.com . make sure you click on " all songs" for that site to show the ones that aren't officially released yet. And then I would recommend sorting by order added if you want to see the new ones that aren't in the store yet.