Get some LP and buy some goodie bags. There's a random chance (about 20%) that it could have Ambrosia.
See the wiki for a nice LP chart (bags cost 300 LP each):
http://www.fantasicawiki.com/wiki/Leana's_Exchange_Shop
Edit: Also, this thread is in the wrong section. It should be in Game Discussion. Encyclopedia is for in-depth guides and the like.