You cant
Actually, you can.
Just do one of these:
1. Trade on the GTS
2. Ask your friend to breed theirs, and give you the egg
or start your adventure get your first starter trade it and do this one more time to get all the starter Pokemon
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No not every pokemon. You can't catch the starter Pokemon and many of the rare pokemon, you have to trade with Diamond. sorry ...
You can get a Cyndaquil without trading only by transfering it from a GBA Pokemon Game onto your Pokemon Diamond Version.
no
You cannot get all 3 Starter Pokemon in Pokemon Emerald without trading for the other 2.
You cant without action replay