1) Catch Golden Whales. They're REALLY not that hard to catch, you can catch them at Fossil Beach at the easternmost fishing spot(to the left of the rock where Zoro and Sanji stood, it's blocked by a rock; I forget whether it's normal or Steel, though), and they fill up two bars of Gold-Component OP's a pop. the only requirement is that you need to max out your fishing rod(materials for line and strength upgrades are also not difficult to collect). Even if your just past the Silver Mountains(which is when you unlock Gold-Component OPs), you should have enough Steel Stones for the final strength upgrade(provided you didn't waste them on OP conversion).
NOTE: You can also catch them at the Plains to Adventure near Sunny, but I prefer Fossil Beach since I never bagged a GW, or even so much as had a GW bite, at the PtA fishing spot. You'll obviously know you've bagged a Golden Whale if it drains your Fishing Rod's strength faster than any other fish you've seen.