Few questions about finding items after battle

[Alneyan]

Fate said:
I thought unique items were guaranteed to be found?

Unless things have changed a lot, there are two kinds of such items: artifacts that can be forged at level 8, and unique items found on special commanders like Solaris.

The latter kind requires Construction 12, so the odd of finding them is higher than 100%; I've yet to see one of those items disappear myself (except by lack of slots, of course).