There are two places to get it.
Snowpoint city
Celestic town
You need to have Pearl or trade with someone who has Pearl.
In Diamond you can get Dialga, but you find him in the Spear Pillar after you beat Cyrus of Team Galactic. Im Pokemon pearl you find Palkia.
You can't find tangela in diamond or pearl you have to transfer it over through Pal park
Whack-a-Hack.com
Find the HM on Route 217
where do i find a totodile in Pokemon diamond/pearl on nintendods
you get the manaphy egg in Pokemon rangers and send it into Pokemon diamond or pearl
You need to have Pearl or trade with someone who has Pearl.
In Pokemon Diamond/Pearl, you find a old man at route 212 with a Leafeon.
Pokemon Number 149 (Dialga) Cannot be found in Pokemon Pearl, he is only available in Pokemon Diamond, where as Number 150 (Paulkia) cannot be found in Pokemon Diamond. If you need to fill the spot to complete the PokeDex, you can see #149 from a lady in Celestic Town.
You can find Aron only in Diamond.
you can only find a cranidos on diamond and a shieldon on pearl
To get a Manaphy in Pokemon Diamond you have to get Pokemon ranger and defeat it and you have to trade it to Pokemon Diamond,Platinum or Pearl.
Do the same thing in Pokemon peaRL
check serebii.net
You can't get Zapdos on Pokemon Pearl or Diamond but you can migrate it from Pokemon LeafGreen or Pokemon FireRed.
You'll need to trade it from Pokemon Diamond, because it isn't in Pokemon Pearl.