Other things, Rowena sells the 3 Celestial ink for the next phase into novus. And there is an NPC that will have you do a daily roulette (expert or high level) for alexandrite.

You can farm alexandrite off fates( enjoy your 2%drop rate), but it requires you to have an ANIMUS weapon equipped. Its also a low drop rate, and you have to be on that portion of the quest line to make it drop, just like the atma.

The alexandrite is for materia melds to the new scrolls. You start with level 1 materia melds and go from there.
This is all I know.