Final fantasy XIII - How/where can i get Ethersols?

I am using the summon then Death method to farm on Adamantoises cuz I am too weak to take them on by brute force. It gets tiresome to have to change my party to fight some other guys to get enough TP to summon before deathing with Vanille. Where can I get some Ethersols? Btw, ya can't buy them at any of the shops.