you can catch them on Pokemon pearl, diamond, platinum, and one or two are found in Pokemon rangers and can be transferred to your Pokemon pearl/diamond games. Also Pokemon can be transferred from and of your Pokemon DS games, such as Pokemon leaf green. To transfer your Pokemon from a gameboy game you have to go to the palpark which you get after you complete the sinnoh pokedex.
only with action replay!!! there is no way without action replay
You use an action replay.
You can't without an action replay
Mystery Gift.
you use an action replay
You can't.
You can't get the Secret Key in Pokemon Platinum without Action Replay, unfortunately. You can get Action Replay from most major websites.
where to find a azure flute without action replay and cheating in pokemon platinum
you have to trade/migrate it from a different game that has a deoxys or buy a action replay
You can't.
Sadly, no.
You don't