Can you spawn special villagers?
Just build more houses of the normal type until you get a blacksmith. The profession of a new child is random, and independent of its parents' professions.
you can use this:
/summon Villager ~ ~ ~ {Offers:{Recipes:[{maxUses:#,buy:{id:#,Count:#,Damage:#},buyB:{id:#,Count:#,Damage:#},sell:{id:#,Count:#,Damage:#}}]}}