By action replay or events that that come rarely
The event scene in Pokemon Pearl where the player meets Professor Oak on route 224 is part of a Nintendo-sponsored special event in order to obtain the legendary Pokemon, Shaymin. The player must be involved in the special event to obtain the key item called Oak's Letter, and afterwards Professor Oak will appear on route 224.
Unlike in other games you just have to see the Pokemon not catch them but when professor oak gives you the natinal pokedex you have to catch the Pokemon
After you see all the Sinnoh Region Pokemon, go to the Professor, and he will give you the National Pokedex, which includes Pokemon from the Kanto, Hoenn, and Johto Regions.
You can obtain Swinub from the swarm in Route 217 in Pokemon Pearl.
there is no cheat
No.
you can't obtain it you have to catch it by yourself
Obtain 200 Pokemon in Pokemon ruby, sapphire or emerald, then go to professor birch and you get to choose one of the johto starters, then you migrate the starter you chose to Pokemon, diamond, pearl, or platinum.
there are 150 kinds of Pokemon that you can see and/or obtain. Unless you have friend trade you Pokemon that you can only get in pearl to you, you'll never obtain them all. In Pokemon diamond and pearl all you have to do is see the Pokemon and you get its data unlike the older versions where you have to obtain them.
in Route 224
Migrate it.
Yes