Bows have a separate "custom crafting" rule that has to deal with the strength bonuses one can use while wielding them.
You could also use the rules on page 79 of Tito's guide which tells how to craft weapons of remarkable durability that also have +1 to hit and damage, etc.
The phrasings there do not specifically indicate melee weapons IIRC, so presumably bows could be crafting using this system.