How about a sword +1 vs. armored opponents? The game already does this with the axe of hewing (+2 vs. shield using enemies). So consider the following ready to use weaponry:
ELVEN BLADES are non-magical, but add +1 against regular armors owing to its superior craftsmanship. These are highly sought after by noblemen and collectors alike and may be found or won.
MAGIC SWORDS +1 VS. ARMORED OPPONENTS are exceedingly rare and include magical armor, excepting perhaps those, like champion mail, having non-standard abilities. The referee can decide here.
|Armor piercing blades are deadly, |
but only against fully armored opponents...
ENCHANTED SWORDS +1, +2 VS. ARMORED FOES are even rarer still, the latter bonus working only against magical kinds.
Obviously, this opens the way to special armor types:
DWARVEN PLATE is non-magical and only usable vs. magical armor piercing attacks, but also the thrusting move from the Fear!, Fire!, Foes! supplement owing to its superior workmanship.
Note: The referee can assign value per their campaign...
Armor penetrating weaponry is easily achieved using these simple mechanics. And, obviously, the referee is free to fabricate others, with no limit to what they might do, so keep your blades sharp!