Steel one from a trainer
If you want a totodile you must have pokemon emerald and you must have the pokedex completed then once you have completed the pokedex fly to new bark town where you got your 1st starter then go and talk to birch he should be in his lab talk to him then he'll look at your pokedex and when he see's that you have completed it he'll give you the nationaldex and he'll let you choose one of three pokemon cyndaquil, chikorita, and totodile, pick the one you want and then if you want to migrate it to either pokemon D/P or Platinum then you nationaldex have pal park unlocked in one of the pokemon D/P or Platinum then have the starter you want to migrate to one of the games in your game boy slot then start up the ds pokemon game hit migrate make sure that the starter you want is in the pc then click migrate for whatever game is in there and choose 6 pokemon you want to migrate but be careful because you can only choose 6 a day! Then after you are done choosing your 6 pokemon hit migrate to D/P or Platinum then on your ds pokemon game go to pal park and go catch the pokemon you migrated and there you go you now have a brand new starter! =)
Theres no trainer who has a totodile.
You find somone with a totadile and use gts or download from coloseium
Apparently you have to complete emerald johto dex, and then go to prof, and he will give you a choice of all three starter pokemon off of crystal silver and gold?
Get a feraligator from coliseum, then transfer it to ruby/sapphire, then pal park it to plat