Here are some places you can find Jade Grass:

Younger brother saves companion - Chang'an
Pass the Far Miss - Holy Village
Liz's Cat - Domremy (France)
Terrific Pearl - Domremy (France)
Make a Fire in Revival Isle - Revival Isle
ET's Intrigue - Sea Channel
Kitty in the Well - Yamataikoku
Who Stole the Badge - Cook's Fleet

Also, here is a link to a guide from WLO forum:
http://forum.wl.igg.com/viewthread.php?tid=8450...

Also, I believe you can get them from magical eggs and colored chests.