Characters with Forge Weapon or Forge Armor talents may hire their services out to other PCs at 25sp per rank. Downtime spent must come from both PCs. Because downtime costs 30s a week this means it is not profitable to sell services to other PCs until you have two or more ranks in something.
NPC Weaponsmiths are available, but charge 50sp per rank. They roll Step 6+Rank, and unlike PCs, will not spend Karma on their attempts.