I can't find it either. There's a good possibility that its hardcoded into the game.
From what I can tell, there are a variety of factors that go into an identified item.
1) In the TreasureTable for a given weapon/armor, it says how likely it is for a dropped item to be Normal, Magic, Rare, Legendary (or unique)
2) The ItemType.txt in the Public/Main/Stats/Generated/Data/ folder describes what boosts that the various categories get (Magic items for example can either have a Small + Normal boost, Normal + Normal boost, or a Large boost)
3) The DeltaModifier.txt in the Public/Main/Stats/Generated/ folder defines all of the possible boosts available.
4) When an item is initially obtained, if it's Magic+ in rarity there is some sort of chance that it's in an unidentified state. The boosts are either already predetermined at this point, or are determined when an Identifying Glass is used (save/reloading to see if a different result comes can test this)
It would probably be a good idea to use Norbyte's tool for Save Game editing and see if there's anything special about an unidentified item in the inventory.
