it depends on which gold you are talking about.
in original you talk to a fisherman and he gives you one but might be wrong
I am not sure in heart gold but try above i dont have heart gold
Chat with our AI personalities
On route 12 in the kanto region somebody gives it to you
if Pokemon gold use good or super rod in oivine city on Thursday.
You have to go to Kanto and fly to Lavender Town. Go South where you will find a bridge-like walkway. Go down quite a bit and you will see a small house. The Super Rod is in there.
Pallette Town with the Super Rod. (Yes, you need the Super Rod in Fire Red.)
super rod route path to cinnnabar