Actually to be complete correct with you but you actually automatically have the national dex all you need to do is catch a kanto Pokemon super easy ain't it.
I don't think you can, in emerald you need the nationaldex and POW! it's open but in ruby and sapphire you can't.
whe you get the super rod [which meens you need the nationaldex] go to victory road and fish there and after a while you should have one this works 60% of the time
94
Starly.
You have to migrate it from Pokemon Ruby, Sapphire, or Emerald but to do so you need to obtain the nationaldex first ummm.... there's another way to get it, it's at route 210 north but you need to have a pokeradar=) hope that helped
it is number 421
After you defeat the Elite Four go to sandgem city and talk to professor rowan and then professor oak will come they will talk then give you the nationaldex
u have to beat the nationaldex
After you get the nationaldex you find it in the great marsh
You have to catch every poke on in your normal pokedex
# Migrate It(Nationaldex needed)
He is still in his lab in Pallet Town.