Additional Info
I believe the Flag: Alliance (Standing) decoration is a promotional item that all players can get for free from their in-game mailbox once they gain access to the Knights of the Fallen Empire expansion, even long after the expansion was launched. This means this decoration is not available to free-to-play players as they do not have access to that expansion automatically. You can get a free copy in your mailbox for every character you create.
It seems to have been available on the GTN for a short time. I’m unsure if it is still sellable. Discussion Thread