Some advice on where to find my missing items

There's a sort of volcanic pool a bit down and to the left of Camp Caldera, and I had a lot of luck searching for shells there. It's a purple version of the orange shell next to. And that first treasure is another silver (or maybe tin?) version of the eyes of Sulani - as far as I can tell, it's only the value of the item that is different. I don't remember where I got that - maybe fishing, maybe beachcombing for trash. Sometimes the 'common' items are the ones that will drive you batty trying to complete a collection.

They didn't get terribly creative with the naming on the collectibles - I've had to be careful to make sure I only sell duplicates, since the names are the same and they look the same.