Board Thread:General Discussion/@comment-24738602-20180512192746/@comment-4503347-20180512194718

Yes, unfortunately. Digital distribution for Ace Combat X, Joint Assault, 6, and Assault Horizon, together with their DLC, have been taken down. If you already own any DLC, you can still download them, but you cannot purchase any that you haven't yet owned.

http://acecombat.wikia.com/d/p/2817749936450308733