Adventure mode, as it exists currently, really only has support for Humans and Human towns. This means that finding Steel weapons (there is nothing better) is quite bothersome. There are two ways you can try to get steel weapons, however.
Kobolds steal weapons from other civilizations, so they can have steel weaponry if they've been harassing dwarf civs. However, Kobolds tend to starve during Worldgen currently, so you might want to try adding the [NO_EAT] tag to them if you want a non-dead Kobold civ in the first place.
- Find a Night Creature Lair near a Dwarf City
Night Creaturs go out and raid nearby towns, taking the possessions of their victims back with them. If they raid a Dwarven City, this means they have a possibility of having a stockpile of steel treasure in their lair