I need help upgrading to Nook's Cranny!

Hi! I just started and have had HORRIBLE luck getting the iron for Nook's cranny... in the 5 islands I've visited, I've only gotten 4 pieces of iron and I spent three of them before I was told about the shop! I'm a beginner but I have a lot of sea creatures, wood, etc I'd be willing to trade. Thanks to anyone open to help! :)