Song of the Sea is currently free for Amazon Prime subscribers in the US
I posted this in the Song of the Sea/Amhrán na Mara thread the other day, but the thread is two weeks old, so people may have missed it.
Song of the Sea is currently available on Amazon Instant Video in the US, and is free if you are a Prime subscriber.
I don't think they have the Irish audio track available, but there are some snippets of Irish used even in the English language version.
Even though it isn't fully in Irish, it's still a beautiful example of Irish culture. The studio's first movie, The Secret of Kells, is also available on Amazon Prime and Netflix, and even though it only has a bit of Irish, it's a great watch.