http://www.serebii.net/pokedex-rs/
you need to find 210 Pokemon to complete the pokedex
You have to lock it up on the pokedex.
you find all the Pokemon
you see all the Pokemon in platinum and trade from your other games like emerald, blue, fire red etc and that is how you find all Pokemon in platinum.
you have to find and catch all the pokemon in emerald....it might take a little trading...
you need to run into it in the wild on a hunch.
Find all 210 regional Pokemon to complete the Sinnoh Pokedex. Then, talk to Professor Rowan in his laboratory.
The Safari Zone, you idiot. After you defeat the Elite Four and get the National Pokedex.
Try this: http://www.serebii.net/pokedex-rs/
You can find Pokemon from the Heonn Region and after you beat the elite four and go to Professor Birch for your Pokedex update, you can find Pokemon from different regions in the earlier games.
You have to go into tall grasses, caves, water, and swampy grasses to find Pokemon. If you capture the Pokemon, they'll automaticly add to your Pokedex. If you complete the Pokedex and you got to Prof. Birch, Prof. Oak or whoever, then you can get a prize.
http://serebii.net/pokedex-rs/ Copy that link into your Browser and it will take you straight to your answer. Hope I've helped.