I don't have an official tab, but I did pick up what I could by ear.
I am not sure if I play it in the same key as the Shields, but I play the intro riff as:
Low E string - 1 - 3 then open A
Then the whole song is Bb Maj, Gm, Cm, F Maj.
The only thing that changes is when you get to "Oh what can I do," you play each chord for twice as long before going to the next one.
It truly is a wonderful song, I cannot believe an official tab hasn't been posted yet.