Well on Pokemoncrater there are dark pokemon that you can find while walking around. When you make a file on the web, if you have the time, you can wait until you find all the pokemon in dark version.
You Have To Do Every Gym ANd Then Get To The Elite Four And Do The Champion. If You Want To Complete It 100% Then Get Every Single Pokemon Aswell(:
Not Every Single one
to catch zapdos in pokemon black you have to have every legendary pokemon
go to serebii.net
You see every single Pokemon, Google this "How to see every Pokemon in platinum DS"
There are shiny Pokemon in every Game.
trade a lot
The fastest way is to collect every pokeon in dimond /pearl or platinum then transport every last one to black and white then collect every black and white native pokemon
you cant get every legendary of Pokemon without cheats or migrating and trading with people
Every single Pokemon except ones with no gender and legendaries.
Buy every game and find out.
find them