No, you must make trades with Pokemon red, blue, and silver to get 249. Mew(#151) is only given out by events or hacks.
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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.
No unfortunately you have to trade some Pokemon for them to evolve so you need some one with pokemon crystal, sliver, or gold to trade with.
Catch 'em all
I think you can with action replay or pal park. But the rest is trading
You can not catch any of them in black or white, but I think that you can catch all 3 in diamond.