Well, with the arrival of the “Lost Memories” event, you can jump on that chance. It launched on October 21st and lasts until October 31st.
Your rewards for beating the event include being able to recruit the pair as well as getting their Memory Crystal’s to break their level cap (if you already have them you’ll get Greater Growth Eggs instead). “Also, look for Cloud’s Memory Crystal II in the upcoming + Dungeon event,” the event’s description warns.
But wait, we’re not done quite yet – there’s a chance to recruit yet another Final Fantasy VII character in this event. If you beat the bonus quest "Complete Temple of the Ancients Classic (VII)" you also get a chance to recruit Aerith.