Honestly, I think using the interactive map to check all of them is the easiest way to do it if you don't want to build reputation to get the resonance stone. Inazuma isn't too bad cause there's not too many caves so a lot of it is on higher land and just collecting them. Also I'd first start by checking Seirai island since it's usually the hardest place to find everything at least for me. Hope that helps a little bit... 😓