National Pokédex Help

I need Diancie, Celebi and Darkrai. I have the National Pokédex Done on my main device, but attempting to do it again for a friend that never has time for Pokémon. He wants Original Form Magearna, I can get everything else myself (kinda- I'll just trade on Pokémon GTS for everything else), but need help for Celebi, Darkrai and Diancie.