You have to go to an event, sadly.
Bird Person, do you actually have Diamond now? If you do, I could get you a wide variety of Pokémon. I have a Level 73 Haunter with great moves that I would hate to see go to waste (of course, you'd get a Gengar, but that's not such a problem, is it?).
And to all other people, I now have Raikou. Once I drain the game, I'll go after Entei. I expect to see a Suicune out of somebody! I still can't find my old LeafGreen cartridge (which had Suicune), but I don't miss K.B. Ghost anymore. I have a female Gengar that is taking his place at my left hand. She's special-- you'd have to see her to know why. Also, I have more than enough Porygons, Eevees, and more. Just ask.
...I still need a Latias.