As far as I know, the only gen 4 game you can get Hoenn Starter in is HG/SS:
I can't remember how I got Hoenn Starter but I think it goes something like this:
After defeating Red, you should go to Magnet Train Pass. Talk to Copycat girl in Saffron City and then go to Vermillion City (By bike or Pokemon that knows fly)
Talk to the fat guy. He should give you doll.
Now, give Copycat Pokedoll.
Now talk to Steven.
He will give you Hoenn Starter based on color stone.
Green is for Treecko
Red is for Torchic
Blue is for Swampert.
But, also there is other way to get Hoenn Starters:
By migrating from Ruby/Sapphire/Emerald or any other gen 3 game you have Hoenn Starter OR Starters in.
For gen 5, I think that Poke Transfer Lab might work if you have Hoenn Starter in Gen 4 Game.