Staff of Rynn +4 (Adventure Mart)[...]The next reason (game balance) is about the powerful items, that many stronger opponents wield as "non-droppable". If you would get them earlier in the game, it would kill much fun later (example: Kangaxx, the Demi-Lich is only beatable by +4 or higher enchantments, and such weapons cannot be found before the Underdar in the original game.[...]
Mace of Disruption +2 (Bodhi's Lair, ch. 3, + illithium)
Flame Tongue (Druid Grove, Trademeet quest)
War Hammer +1, +4 vs Giantkin (de'Arnise Keep)
Carsomyr +5 (Windspear Hills)
Staff of the Magi (Twisted Rune)
All the above have +4 or +5 enchantment, and are obtainable before the Underdark, even in the original game.