These keys may appear unusual to a British locksmith, but they would seem to be very common in Portugal. If that's the case, any local locksmith would be able to duplicate one quite easily and quickly, I would have thought.
These keys are not likie the British keys in more than one way. It seems to me that they are not machined for pecision as are out British keys, but either cast or forged. If cast, depending on the metal used, they might be rather brittle. Drop them once on hard ground and they might shatter. However a cast key would be dead easy to make. Using a split box, fill with the correct sand, tamp well down each half, smooth the surface, then press the key firmly up to its centre line in the sand of each box, so that an impression is made of both sides of the key. Clamp the two halves together. make an entrance pouring hole and an exit hole.
Heat the chosen metal (Iron would be the easiest, I think) and once thoroughly molten pour into the mould. Allow to cool and open the box, tapping the side to allow the key to fall out. Fettle ... and Voila a new key. It could be hardened or subjected to any number of processes to strengthen it.
Forging would, I think, be more difficult, but would provide a tougher key. I have worked hands on in a foundry and cast metal there, but I have never forged metal except a la blacksmith, by hand. I have watched the forging process many times.
I think this key might have been cast in a manner rather like the lead sodiers kids used to make. Then treated to strengthen and case harden.
