A note on efficiency:
Here's a famous quote by the inventor of Quicksort: "We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil."
You can find a fuller quote in the docs: https://docs.godotengine.org/en/stable/tutorials/optimization/general_optimization.html#principles
But in short, focus on correctness (your code does the right thing), rather than speed (unless it causes noticeable frame drops).
(END OF RANT)
Now about your question:
your approach is basically what the find method does. It's quite possible that the find method is faster because it is implemented in C++ rather than gdscript, but I didn't measure it and unless your array contains at least a few hundred elements, I doubt you'll see much difference.
However, I don't really understand why you need to find the value if you already have it. What I mean is if the statement
if value == specific_value: equates to true, why not just return specific_value instead of going through the array? You've already proven the two values are equal.
Maybe your example is incomplete. Maybe your code is more like this:
func get_item(item_name: String):
for item in self.item_list:
if item.name == item\_name:
Although calling the find method like this:
self.item_list.find(item_name) wouldn't work, since the item list contains items and not strings. I am a bit confused by what you want to do. Could you share your whole script where you handle the array?