A better question would be what Pokemon CAN'T you get. Just about all of them are obtainable, except for the following:
The three Kanto starters and their evolutions
Mewtwo
Mew
The three Johto starters and their evolutions
Murkrow and Honchkrow
Misdreavus and Mismagius
The three Johto Legends (Entei, Raikou, Suicune)
Lugia
Ho-Oh
Celebi
The three Hoenn starters and their evolutions
Trapinch and it's evolutions
Clamperl and it's evolutions
Latias and Latios
The Weather Legendaries (Groudon, Kyogre, Rayquaza)
Jirachi
Deoxys
Glameow and Purugly
Stunky and Skuntank
This leaves a grand total of 56 Pokemon that are unobtainable by normal means.
There is no rental Pokemon in in Pokemon platinum
In the National Pokedex in Pokemon Platinum Mawile is Pokemon 303.
The 111th Pokemon on Platinum is Garchomp.
Nobody in Pokemon platinum has a charmander.........
You can't get Thunderus in Pokemon Platinum at all. By then when Pokemon Platinum was made, no one knew that Pokemon Black and White were going to be made.
There is no rental Pokemon in in Pokemon platinum
You cant get Pokemon from Pokemon ranger to platinum!
how to get a togepi in Pokemon platinum
There is no grunt that you can give a Pokemon to in Pokemon platinum.
buy the Pokemon platinum book
yes there is a new Pokemon in Pokemon platinum. its name is Arcues.
The 151st Pokemon is Mew and is unobtainable in Pokemon Platinum.
In the National Pokedex in Pokemon Platinum Mawile is Pokemon 303.
That pokemon is Azumarill in pokemon platinum in the national pokedex
There are a lot of events on Pokemon Platinum.
No, you cannot get Jirachi in Pokemon platinum.
Heatran is a ledgendary in Pokemon platinum.