Verified answer

Except for the added note about the Chimera Brain, this info is cited directly from KADFC's (Fabian Chang) "Item Database" at GameFAQs (see my source).

***Steal***

* Nemesis

***Reward***

* Capture 10 of each monster and defeat all monster creations at the Calm Lands Monster Arena

***Drop***

* Spectral Keeper (Zanarkand Ruins)

* Seymour Flux (Inside Sin)

* Land Worm (Inside Sins - Point of No Return)

* Omega Weapon (Omega Ruins)

***Bribe***

* Chimera Brain (Calm Lands, usually northeast of Rin's shop) - 196,000 Gil

***Found***

* Chest (Home: Living Quarters)

* Chest (Gagazet: Mountain Trail)

* Chest (Inside Sin - Sin: City of Dying Dreams)

***Prize***

* Omega Ruins - Open the first Chest

* Omega Ruins - Open 7 Chests

LOL i love FFX i remember it lol i cant believe people still talk about help for it cool. Umm i dont remember they were moderatley rare if i recall.

Oh God they are HARD to find. I cant remember exactly but if you go to www.gamefaqs.com they have all sorts of walkthroughs and such to help you get them.