you dont
you cant find raiku in Pokemon pearl just Pokemon gold
listen to me SHUT UP!!!!!!!!!!!!!!!! I know how to get every Pokemon but I won't tell so LEAVE ME ALONE
catch it in the wild
You can't.
NO you cant catch syther in Pokemon pearl
You can't catch a charizard in pokemon pearl.
You can catch Mewtwo, Suicune, Entei, Raiku, Ho-Oh, and Lugia.
you have to beat elite 4 then catch all unowns.
You have to trade or migrate. You can't catch them in diamond.
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
you can certainly catch Dioxies in the game Pokemon pearl
It's impossible to catch Jiratchi in Pokemon Pearl version.