Chikorita, Totodile, Cyndaquil.
You can only get the Johto starters by trading from Emerald or XD.
No way you can't get a johto starter Pokemon in Pokemon leafgreen. The only way is to trade with someone to get it.
You can't get to the johto region in firered.
By trading for them.
The Johto Starters are Totodile which is a Water-type, Cyndaquil which is a Fire-type and Chikorita which is a Grass-type.
one of the three johto starters: totadile, cintaquil or chikorita
after you finish your hoen pokedex and boy it that hard you get to choose one of the three johto starters and that's it!
Basically, -just- and I use the term loosely, obtain all Pokemon obtainable in Emerald/ruby/sapphire, on such games, then choose a johto starter (Birch will call you) and trade. Only way, sorry.
Only emerald can get a johto starter however you can trade the johto shadow Pokemon from Pokemon colosseum then breed them in sapphire to get the johto starters you can also trade the johto starters directly from Pokemon xd gale of darkness.
Mudkip Torchick Treeko (hope this helps)
You can't.
Pokemon Soulsilver and Heartgold has the 3 original starters, which 1 of them can be obtained after getting 16 Gym Badges. (8 from Johto and 8 from Kanto) For GBA, which also can be in the DS (Not in DSi and the 3DS family systems, though.), it would be Leafgreen and Firered.