were can I find frost gems cause i can't get them in the black and white places

can someone please tell me how to beat junk heap and poster boy and cargo climb in twilight town. Can't do it!!! And how do you finish Olymipus colisium those are the two levals I have left!!!!

Is there a way to actually be Riku, and if there is can someone pleaze share it with me. Also how do you put in cheats. And what the heck is a gameshark and do they cost money??