How do I catch Arceus, Shaymin, and Darkrai on Pokemon Diamond?

Question

I've read this FAQ thingy and it says go to a PokeMart and talk to a guy wearing green. I tried that and I couldn't find a guy wearing green in any PokeMart. Is it correct? I've also been reading you have to HAVE to have an Action Replay. Is that correct? Anoter thing I've read is that you can't catch them at all. Is that correct?

Answer 1

where is newmoon island and the action replay?