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Bulbapedia says that you get a Togepi Egg from the champion in Eterna city and an Eevee the first time you go to Hearthome city from Bebe in Platnium.
It also says that Yanma are Uncommon and that Scythers are rare near 215. Also, the Elite four in that game also use Post-national Dex Pokemon. Does this mean that I can get a Vaporeon or a Yanmega before completing the Sinnoh Dex?

The Sinnoh regional pokedex is bigger in Pokemon Platinum. (Nintendo has never done this before.)

The first 151 pokemon are still exactly the same (#151 being Manaphy) and in Pokemon Platinum there are 210, meaning there are 59 more. Those new pokemon are:




As you can see, Eevee, Togepi, Yanma, Scyther... they have all been added to the Sinnoh pokedex. This means you *need* to see a Vaporeon and a Yanmega *in order to complete* the Sinnoh Dex in the first place. (Actually acquiring them is much better.)


(Note that, in Pokemon Platinum, you can get credit for seeing Manaphy thanks to a book in the Pokemon Mansion.)


The Elite Four (and the Gym Leaders) both use Sinnoh pokemon ; they just have 59 more to choose from. (Some of those 59 were probably intentionally added to bring better pokemon to the Elite Four / Gym Leaders.)

As for the location in-game of pokemon, I'm firing up my Platinum (Japanese version) to see what it says...


Scyther: The in-game pokedex indicates that Scyther shows up on Routes 210 and 215. (Its evolved form, Scizor, does not appear anywhere in the wild.)

Yanma: The in-game pokedex indicates that Yanma shows up in The Great Marsh (aka The Safari Game.) (Its evolved form, Yanmega, does not appear anywhere in the wild.)

Togepi: The in-game pokdex indicates that Togepi shows up on Route 230 (post Elite Four), but you can get one earlier from The Champion in the form of an egg.

Eevee: The in-game pokedex indicates that Eevee can be caught at the Pokemon Mansion, but you can get one easier from the girl that runs the computer system.

It's an event-only item. However, Nintendo is finally using the Wi-Fi Mystery Gift feature to give it away which means that we should be able to get it over the internet. (That's what they've been doing for Pokemon Platinum.)

It's why I was able to get the Secret Key for my Japanese Pokemon Platinum game despite being here in the U.S. 3nodding (They've also given away the Membership Card key item which allows you to capture Darkrai in-game, and sometime next month they'll be giving away Oak's Letter so I'll be able to catch Shaymin in-game. blaugh )