How do you get Nidoran in Pearl or Diamond?

To obtain a Nidoran (both male and female) in Pokemon Diamond and Pearl, you must use the PokeRadar in the grass of Route 201. It will take a while to find the two Pokemon (the female Nidoran is harder to find in Pearl and the male Nidoran is harder to find in Diamond), and they have a maximum level of three.

Of course, you could always migrate the Nidoran to te Pal Park from Pokemon FireRed or LeafGreen.

YOU COULD ALSO JUST PUT A NIDOKING/QUEEN IN THE DAYCARE WITH A DITTO AND WAHLA YOUVE GOT AN EGG!

ACTUALLY A NIDOQUEEN CANT BREED