The only missing piece of the puzzle for those that are stuck running out of unused share %, is how to decrease the orange bar shares. I think they go down exiting and not completing dungeons, but it's tricky doing that method because when I tried that once, it caused not only the orange shares to go down but also the shares for the landmass I was working to increase.
Well by default, normally people don't need to resort taking shares from orange bar to have enough shares to unlock the Versus ______ event in Explore. But I guess it depends what quests people have been doing and what they've been trying to increase/decrease.
Anyway if it still doesn't appear just keep increases shares if you can, sometimes the bar is hard to gauge if it's at 20% or 30%. My bar looked like it was near 40% when the event appeared in Explore section. viewtopic.php?f=47&t=3612