* From the Fisherman in Accumula Town: This is the most common way to get a fishing rod. Once you reach Accumula Town, go to the house in the northwest corner. The Fisherman inside will give you the Old Rod for free.
* From the Fisherman on Route 4: This fisherman will give you the Good Rod after you have defeated the Gym Leader in Nacrene City.
* From the Fisherman on Route 13: This fisherman will give you the Super Rod after you have defeated the Gym Leader in Mistralton City.
* From the Fisherman on Route 16: This fisherman will give you the Master Rod after you have defeated the Gym Leader in Icirrus City.
The Old Rod is the weakest fishing rod and can only catch basic Pokemon. The Good Rod will let you catch more powerful Pokemon. The Super Rod can catch the most powerful Pokemon, while the Master Rod is only used for specific fishing events.
Remember that you'll need to buy Bait in order to use your fishing rods. You can buy bait from the fishing shops in various towns.