I don't think anybody would necessarily have extra of any of those lying around.
Darkrai... although I got enough to have extra Darkrai when the event happened, I don't really have any extra ones now. The only known source of legit Darkrai in the near future will be
Pokemon Ranger BatonnageLugia... that's a very specific Lugia you're asking for and we don't have a lot of long-term dedicated pokemon players in here (IE people like me except they've been devoted for long,) The best I would be able to do is obtain a Lugia from XD: Gale Of Darkness, but I haven't playing through that game yet to obtain one for myself so I can't really say how much it would "cost."
Shiny Wigglytuff... well, I'd guess that people aren't likely to just have one lying around. Somebody would probably have to intentionally chain one for you from the Trophy Garden, and that could still take some time.