No, Totodile can only be acquired by choosing it at the start or by trading.
Don't listen to him. You can catch all the starter pokemon and their evolutions on Victory Road.
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You cannot catch it in the wild, obtain it, or find it in a special place. You'll need to trade for one or transfer it from the older DS Pokemon games.
Unfortunately, you can't catch a Chikorita in the wild. You'll only be able to find it if you choose it as your Starter Pokemon or you chose a Totodile as your Starter (in which your rival will choose the Chikorita). Or you can trade another Pokemon for it in the GTS.
It is not possible to catch a wild Turtwig on Pokemon Diamond. It is generally impossible to find and catch Starter Pokemon in the wild. This was a mechanic designed to encourage player interaction for trading.
catch it in the wild
You cannot catch wild Chikoritas in any official Pokemon game.