Add a quiver item. Ostensibly in the tool class, could either take up a new equipment slot, or take up the shield slot to prevent you from wearing a shield at the same time the quiver is equipped. It’s not actually a container, and just “holds” whatever is in your existing in-game quiver. While equipped, it adds +1 to your multishot, possibly +2 if it is blessed but this may make it too powerul.

Also change the Ranger quest artifact to the Quiver of Diana, a quiver which gives telepathy and reflection when equipped and possibly also prevents ammo from breaking, though it can still erode. When invoked, all projectiles on the level that you threw or fired are magically returned to your inventory, even if they’re being carried by monsters or buried or whatever.