Waiting for rykomatsu to put up more info.
EDIT: First bit of translation from ryko:
RAH System (Hymnos Synthesis)
This title's Hymnos isn't limited to heroines just "singing" them. If you "combine" hymnos parts that are bourne from the heroine's psyche, the player himself/herself can create hymnos. Merging this RAH system and player's actions, the real-time BGM changes, which the Active Music Generation System accomplishes, brings a presence never experienced before (I'm assuming in regards to game BGM). Creating a good hymn and having the heroines sing it will bring effects such as increasing the vanguard's attack power.
Now Playing: Final Fantasy X HD
It has been out for 9 months...
It is still listed at gamestop. If your local shop is mom and pop, then probably not. I don't imagine BB/Walmart etc ever did carry the game, considering that the game sold a total of 30k in NA... it probably is not even worth it for them to place an order.