You can buy the Ultimate Game Cards at Preplayed now. Heck, I even found they sell them at a Walgreens right down the block from me. However the way Ultimate Game Cards work is that they apply it as Crysta to your moog station website. Then, once your free 30 days are up, the balance from the card transfers over to your FFXIV subscription each month, and you (should) get your first 30 day bonus then, and follows the same pattern the next month, etc.
Apparently in Japan they have SquareEnix prepay cards that applies the balance to your subscription immediately, so you can buy 3 months worth and get all the announced rewards so far instantly. But for whatever reason, the US cards have to wait till the 30 days are up to start applying the rewards ;0