Latron is a primary weapon which can be obtained from two ways. The first one is the expensive one, and is buying it with platinum, either in the Market Console you have in your ship or through you arsenal. If this is your option, I advice you to check Darvo’s daily offers. This way, if you buy it you also get, for the same price, an installed Orokin catalyst and a weapon slot in your invetory.
The second way to get the Latron will also be through the Market Console, but buying the Latron Blueprint with credits to craft it later in the Foundry of your ship. This is the most traditional, but also the slowest. Remember that you have to spend credits, both when you buy the blueprint and when you craft it, and, of course, you will need the necessary resources to be able to craft it.