I missed the 20th anniversary Pokemon, but I know that currently you can get mew off of a game called my pokemon ranch and I was wondering if there was anyway currently to get Jirachi? and if so exactly how?
Jirachi can be obtained in Ruby and Sapphire using the US Colosseum Bonus Disc or the European/Australian version of Pokemon Channel. From Bulbapedia:
Pokémon Colosseum Bonus Disc This disc contains previews of Pokémon Colosseum and the movie Jirachi: Wish Maker, as well as a downloadable Jirachi. To receive Jirachi, a Nintendo GameCube–Game Boy Advance cable, an English copy of either Pokémon Ruby or Pokémon Sapphire, and an empty spot in the party is required. With everything connected properly, Jirachi will appear and be transferred to Ruby or Sapphire. The process of obtaining Jirachi can be repeated as long as the save file that is receiving Jirachi has not already used this disc. If the game that is being used to get Jirachi has the Berry glitch, it will be fixed upon receiving Jirachi. It is not required to own Pokémon Colosseum to receive Jirachi.
Pokémon Channel Players can obtain Jirachi in both the European and Australian versions of the game. It can be downloaded onto a version of Pokémon Ruby and Sapphire. After unlocking the full version of The Pichu Bros. in Party Panic, Jirachi will appear, and the mini-movie will be shown above the campfire. The Berry Glitch in Ruby and Sapphire can also be fixed.