Yes, Heartstones, the things that look like a pink crystal. Around the Bedokaan Village like Zorque said.
oh, sorry , this is my second time beating this game, and i still dont know have the things you need to do lol. 8)
You get the schematic a while before you find about the Bedokan, & only the alter mentions Heartstone. Or, don't feel bad, it's not at all obvious.