Harvest moon magical melody how do you get the fishing pole?

It is already in your tool box. To gain upgrades you must use it (in the menu description there should be a level bar showing how much you have to go until a certain level), then buy the next level from the Junk Shop. Or when the blacksmith comes to town, (you can get him by shipping one of each ore and he'll set up shop near the beach) you give him the ore of your choice and the tool and he will upgrade it for you for a lot lower than what you can buy it for. You can find the ores by smashing rocks in either Moonlight Cave or the Lake Cave. (Only available in the winter, you walk across the ice towards it.)