I can't see an appropriate forum to post this on.
The song isn't actually called Rhalgr's Ruin, I did see it listed on the music voting thing Square had but I can't remember the name. It's called Rhalgr's Ruin on Youtube.
https://www.youtube.com/watch?v=WcVgrRkl_Dk
I think this is one of the most beautiful pieces of Stormblood, we only hear it once when Rhalgr's is in tatters. I would love to be able to have this on Orchestion.