You only have one chance at finding any item using Move-Find Item. I really hope you didn't save after that, because that's the only easy way to get a Chaos Blade. For the future, lower Rafa's Brave down to 16 to get the best chance of getting the good item. You can also go as low as 10 if you don't mind getting warnings all the time.

Your only chance now is to find Ninjas at level 98 and 99 (they can most easily be found in HORROR) and hope that they know how to throw Chaos Blades. You need to have the Catch reaction ability equipped to catch them. In case you're interested, the Deep Dungeon Guide by Notti has a full list of catchable items.