You get it by seeing every Pokemon in Sinnoh you can do this by:
1. Completing the game and doing most battles with trainers.
2. Evolving lots of the Pokemon you have.
3. Trading with other people who have the game.
4. Using cheats.
484-500
Mew three is an exclusive to chaos black
you can foud ivsaur in Pokemon diamon in route 225 for your natinal pokedex
The first Pokemon in the national pokedex is a bulbasaur
get a bubasour
he should be in turn back cave after you get the natinal pokedex =)
by seeing all 150 sinnoh Pokemon including palkia.
get 60 in your pokedex and go to oaks lab
The Pokemon Mothim is number 47 in the pokedex(will be different in the natinal pokedex.Hope it helped:)
No, there is not a Pokedex after the National Pokedex in Pokemon Diamond Version.
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
you need to finish the sinnoh pokedex then go to professor Rowans lab and professor Oak will give you it