To obtain the Johto starters them, there's 2 ways. But not via GTS.
1.) Capture all Hoenn Pokemon in Emerald, go to Prof. Birch's lab then he'll let you choose and you can only take one of them.
2.) You can go and find someone who will breed and trade them for you.
As for the other unseen Pokemon that you want to obtain, it's the same to the second way to get Johto starters. I'm sure that there are people here in this forum who are willing to do the trades on Trading Section.
Sorry it has taken me so long to get back to you. unforunately we had a family death the tuesday before Christmas, other then that things are great. I am 66 pokemon short of having a full pokedex. Hey question. Since with GTS you have to have seen the pokemon to be able to find them to trade how do I go about the ones I have not seen, such as cynderquil, and bayleef?
I'm so sorry, I can't find any map for you...
If there's a barrel infront of you, that means you are in a wrong way. You have to keep looking and remember to have Max Repel so you wouldn't be distract by the wild Pokemon.
It's okay, we're friends, right? So I'll help you if I can. If you have any questions you can ask me. But not about the EVs, IVs, best battling movesets, best battling team. I'm not expert in battles, I mostly participate Pokemon Contest. You can call me full time Coordinator and part time Trainer.