Another way to solve this situation may be making some of the unique weapons upgradable by finding some rare materials later and reforge them.
DOS:EE had an interesting approach to this in the form of
adventurer's weapons. You purchased a low level weapon and found upgrade components to it as you progressed through the game.
...Unfortunately the upgrade pieces were generally placed a bit too late which meant you often were 1-2 levels above their level tier. Because of this the weapons' stats were almost always outclassed by random weapons you had looted from enemies or bought from a merchant. Bit of a shame, but I did like the concept and treasure hunt aspect of it.
