What items are only available once?

Question

I noticed that the item Metal Cloak is only available once per game/save state and that means you can only evolve a single Scizor or Steelix. Now are there some other items that occur only once per game and that don't require you to steal it from a wild Pokemon to get a second one?

Answer 1

The items you mean are Evolution-inducing held items. These are often only avalible once in a game. Here is a list: Evolution-inducing held items

Also there are story and basic items you only get once like a bike and so on.

Which Pokémon evolve while holding an item you can see here:

Evolution while hold an item

Evolution while trade and most of them hold an item