The second butterfly chase is only a screen or two past the first. There will be no person to talk to, just look for another rainbow butterfly.

As for Wakka, you can get his weapon from the barkeep in Luca. You will have had to play enough Blitzball for her to give it to you, though...

Here's a link to a whole bunch of FAQs for FF-X:
http://www.gamefaqs.com/console/ps2/game/197344.html