Im stuck on a game Need Help?

Im playing Dark cloud 2 On my playstation 2, .. & no matter what walk-through I pull up online.. I cannot find what im looking for... Im trying to find the "indestructible" coin to recruit Donny. Im going back & forth in my dungeons for hours on end looking.. can anyone tell where to find it, On what level & where between sindain & palm brinks? thanks