This throwing weapon can be obtain from several ways, being the first one the most expensive. This option is to buy this secondary weapon, either in the Market Console of your ship or directly through your Arsenal for 175 Platinum. If you choose this option you will have the Spira ready to use, an extra weapon slot in your inventory and also an Orokin Catalyst already installed.
The second way will be to buy the Spira Blueprint, having after to gather all the necessary resources to craft it. You have also to keep in mind the required crafting time in the Foundry of your ship.