The GTS
1. The PC
2. The Globe. Here you can see the locations of the people you have traded with.
3. The door. Used to enter and exit the Global Trade Station
4. The GTS attendant. Talk to her to start a GTS session
5. The Door to the Trade room.
Located in Jubilife City, the GTS is a boon to all avid Pokemon Collectors. The only problem with it, is that in order to get a Pokemon from another player somewhere else in the world, is to have it a spot in your Pokedex. (meaning that you have to have seen the Pokemon in the past.) A good way to get all of the Pokemon after you've seen them, but not if you need to see any pokemon.
People out in the world LOVE Febas. If you find a person who will give a Febas for a non-event legendary, go for it. Or you could get one from your friend, or catch it yourself. Febas are always a good Pokemon to have. With them, the GTS is at your fingertips.
Even if you had to trade a Legendary Pokemon to get it, this means that once you breed another, you can just trade it for that same Legendary. People will do this. And now, with the inclusion of the Poffin and berry shop in Veilstone, in Platinum, you could possibly have level 2 Milotic. Any Pokemon that you want can be yours.
AND now that I have built up your dreams of a Pokemon trading empire, I have to remind you that you have to have the data in your pokedex. My advice would be to get an old copy of a game that you don't play much, but a newer version, like an old Diamond version, and borrow a friend's Action Replay, and then use the cheat on it to get a complete Pokedex. Then trade between the two games, and put them up on the GTS through that older game.
However, if you don't want to cheat, and I don't blame you, the only way that I see is to go and give your money to Nintendo, at the events.