Afraid I can't speak to that (I'm sure someone else can), but there are several other ways to get them:
1) Find a sage that offers to make a unique item. I have found quite a few of these, but have never had all the items required. There is also a chance it will not work.
2) Nobles that carry items can sometimes drop them if injured in battle. Other nobles scrounging for armour repairs can pick them up, and I presume adventurers searching for items could also (the latter is not personally confirmed, but inferred from what other players with adventurers have said).
3) Perhaps simply searching could find one? Am not sure if this would a new item though, or an already existing one as seen in the above point.
I believe all three of these are correct, but I am more sure about the top two.
There are no monster champions, just undead champions, so you might want to focus on the undead if you want to get a unique that way. My advy created one unique with a sage, and defeated 2 undead champions, or her 3 recommendations.
