After you get the national dex and beat elite4 you go to fight area and go up after you get off the boat and a fisherman who is not moving in red beside the building to route 225 talk to him say yes and he will give you the rod
beat the elite 4, and cynthia, then go to snowpoint city, take the boat, once you get to the fight area, go north and you see a fisherman, he gives you the superrod .
and yes , I copied this ...
At the fight area talk to the fisher man near the cargo
He gives you the good rod not the super idiots...
Beat the elite four, after go to snowpoint and take the boat and go north and you will see a fisherman moving talk to him and hi will give you the super rod
I found were it is but you need the national dex if you don't have one you can't get it I tried but you can if you have the replay cheat I don't have one but you can if you have it.
When you get the national dex go to the gate to route 225 and talk t the fiisherman and he will give you the super rod.
To get the super rod in Pokemon pearl follow these steps. On route 209, you will come across a fisherman, answer Yes to his question and he'll give you the super rod. To get a detailed answer to all the steps visit the following link, and I'm sure you'll find your way out.