Spell casting adventurers would definitely attend to this problem. 1st edition has the 4th level Magic User spell “Enchant Weapon.” That would be beyond the reach of most mid-level parties that have fewer than typical weapons. But I can't help but think this is an under-powered spell for its level. It provides no bonus to hit, compared to the 2nd level spell Strength which lasts much longer and could certainly add to your melee bonus. Other 4th level spells to compare Enchanted Weapon to include Ice Storm, Wall of Fire and Polymorph Other. The d20 spell, Magic Weapon, provides +1 to hit and is only 1st level.
Mechanically, I intend to use these spells to avoid the Christmas tree effect of too many boring +1 weapons. I can limit those weapons, and pay more attention to the ones that I do place. Monsters that can only be hit by +1 weapons will still be a challenge, but not an unavoidable one. They will be a challenge that can be over come by preparation and resource management. A later post will detail potions that also solve the problem.
Evelgraten's Enchanted Edge
Level 1 Magic-User spell. Alteration
Components: V,S,M         Range: Touch
Casting Time: 1 round     Duration: 5 rounds/level
Save: None.            Area of Effect: 1 melee weapon, or 5 pieces of ammunition
This spell enables the touched weapon to hit creatures that are only hit by +1 magical weapons whether they are incorporeal, ethereal, extra-planar or otherwise supernatural. It does not otherwise provide any bonus to hit. The material components are a piece of unprocessed iron or silver ore and a garnet of at least 5 gp value which are touched together during the casting of the spell.
I choose the casting time of a full round instead of a segment because other 1st level spells creating a lasting effect (like Nystul's Aura) are a full round. I felt that the spell should have a material cost, thus the gem and the 'cold iron' was evocative of folk lore.
Level 1 Cleric Spell Alteration
Components: V,S,M, DF      Range: Touch
Casting Time: 1 round        Duration: 6 melee rounds
Save: None              Area of Effect: 1 melee weapon
By means of a boon from their deity, the cleric blesses a weapon enabling it to hit creatures of an opposing alignment (or otherwise inimical to the deity) that are only harmed by magical weapons and providing +1 to hit. Some deities may require recitations from a holy book, but the typical material component for the spell is holy water which is dabbed upon the weapon during casting.
Yes, the recitation is meant to be a Monty Python reference. I modeled this spell after Bless, and the differences between it and the magic-user spell are intentional.