How to import whole category in Dwarf Fortress?
Solution 1:
You can't do it, which is a shame, because other parts of the game do understand the concept. The dwarven and human traders can agree to pay more for 'headwear' next time they visit, and an iron helm will fit the bill just as much as a silk hood. Also your nobles can mandate the construction of 'splints' (any material) or 'bronze items' (any kind).
Maybe later.
The next version of Dwarf Fortress will apparently make major changes to the way trading and the economy work.