From the moment the first episode of Outlander aired on STARZ fans have been gushing about the theme song which so beautifully captures the characters, the time frame, and the culture of the show.
In answer to the question, is the song (by Bear McCreary) available, can it be heard/purchased, I have found it available at Rhapsody.com. It is also available at the iTunes store, search for Outlander – Main Title Theme (Skye Boat Song) [feat. Raya Yarbrough] – Single, by Bear McCreary. (Press play in the player below to hear a 30 second clip, members of Rhapsody can signin and hear the entire song.)