It may take multiple attempts to find a certain item. This means that this item is rare and harder to find. Each item has its own chance of dropping.
If the item you are looking for is on the "You Can Find" list in a location's window, this means that the item will be found sooner or later.

You can try activating a talisman or hiring a friend with the Ranger talent to increase your chances of finding the item. However, be aware that Luck Talismans do not increase the odds of winning a particular item (such as a quest item). They simply increase the odds of receiving any collection items or fixer from the "You Can Find" list.