The Dinkum Thunder Egg Appears randomly on the island but can be found if you pay close attention to the environmental factors such as rain and thunder.
How to find the Dinkum Thunder Egg:
The very first thing you need to be sure of is that it is raining. Once it starts to rain, keep your eyes peeled for flashes of lightning and listen for the sound of thunder. The Dinkum Thunder Egg will spawn in the area where you see the lightning and hear the thunder.
Remember the egg can spawn anywhere on the island so keep following the signs and don’t leave any corner. That’s pretty much it. I hope you found this guide helpful. Do let us know if you find any trouble finding the Dinkum Thunder Egg.