you could go to Via Infinito to cloister 15~19, where the Chocobo Eater is common to appear (it may take time to appear). To get the Anything Eater, you need to do the Chocobo Sidequest with Clasko. There's a link in gameFAQs that explains how to get the Chocobo Cave at Calm Lands.

Copy and paste:

http://www.gamefaqs.com/console/ps2/file/562386/27532

There should be everything you need to know to unlock the Anything Eater. After you get that, going to Via Infinito at cloister 41~50 (Around those numbers), the Anything Eater should appear as a random encounter.