Go to the < of Jubilife City towards Canalave City. In the building separating Jubilife City and the Route to Canalave talk to a person. He will give you the Old Rod.
A Good Rod is available within Roue 209 in Diamond and Pearl.
Route 222
Pokemon Diamond & Pearl: By surfing - Golduck Using Old Rod - Magikarp Using Good Rod - Magikarp and Goldeen Using Super Rod - Gyarados and Seaking Pokemon Platinum: By Surfing - Golduck and Psyduck Using Old, Good, or Super Rod - Magikarp
Magikarp
I don't think there is one. But I do know this! POKEMON DIAMOND AND PEARL- ULTRA ROD IN FRONT ON ENTRANCE TO ROUTE 255 POKEMON PLATINUM- OLD ROD GAVE TO BY CYNTHIA'S GRANDMOTHER POKEMON BLUE RED AND YELLOW- NO ROD FOUND YET
old rod good rod super rod and pie rod
Go through the gate way at the left side of Jubilife City and talk to the fisherman!
only magicarp
NO Such Thing Only Super Rod/Good Rod/Old Rod.
You can catch Lanturn in Pokémon Diamond and Pearl by Fishing with the Super Rod in Route 220.
You can obtain QUILFISH but fishing at Iron Island with a Super Rod.
There is no "mega rod" on Pokemon Diamond and Pearl. There are three rods, the Old Rod, Good Rod and Super Rod. Old rod: fisherman in the house west of the Poketch company building in Jubilife city.Good Rod: Fisherman on Route 209Super Rod: Fisherman on the northwestern side of the Fight Area (only accessible after beating Elite 4)