First, you need to have beaten the Elite Four and the Champion. You also need to have seen each and every Pokemon in the Sinnoh Pokedex. Go to Prof. Rowan's lab and talk to him. Prof. Oak will then come, talk to you and Prof. Rowan, and will give you the Pokeradar. (I have quite forgotten what exactly happened, but talking to Prof. Rowan with the said requirements will activate a scene, and you will get the pokeradar anyway. For a tutorial, look for Dawn/Lucas at route 202 after getting the pokeradar.)
You can't without the Pokeradar.
eterna forest with pokeradar
Route 211 West with Pokeradar.
You have to use the PokeRadar on Route 205
go to sendoff spring and use pokeradar
pokeradar is only at Pokemon pearl , diamond and platinum.
You can't without the Pokeradar.
finish the whle entire pokedex
You cannot get a Pokeradar in Pok_mon White, nor can you get one in Pok_mon Black. You can only get a Pokeradar in Pok_mon Diamond, Pearl, and Platinum
route 210 with pokeradar
vally windworks with pokeradar
eterna forest with pokeradar
Route 211 West with Pokeradar.
Routes 209 and 210 with the pokeradar.
Use PokeRadar on Route 201
Nidorina: roue 211 (use pokeradar) Nidorino: route 221 (use pokeradar)
The Pokeradar is an item that you get in Pokemon Platinum. You get it from Professor Oak after completing the Shinoh Pokedex.