Craftsmen are found in most tube stations, usually near the merchant and apper with the same currency symbol over thier head as the merchant has.
There are a number of items that can be crafted at any one time from a craftsman. The type of items that can be crafted appear at random in sets, for example at one visit a craftsman may have a variety of shields that can be crafted, at another visit there could be a variety of helm armour.
Craftsmen require a variety of base components salvaged from loot for items to be crafted. The type and amount of components needed vary according to the item that is to be crafted.
Crafted items are generally of good quality, either enhanced or rare or possibly legendary items.