Use the GTS and some friends, and be VERY lucky!
you cant
no
There currently is no glitch that allows you to have every Pokemon without cheating. However, get action replay for Pokemon if you really want to cheat.
yes
You'll have to catch them and the last 3 you need a Nintendo event.
You have to battle every Pokemon Trainer in Sinnoh.
you had to get alot of them through events or mystery gifts
in every pokemon game you get one master ball before the leauge
There is no code for that, unfortuneatly.
A Pokedex cheat
yes, if you're willing to put it in your action replay DS
Yes there is but you need an action replay.