This weapon can be obtained from two different ways. The first and most expensive one, is to but the Scindo for 150 Platinum directly through you Arsenal or the Market Console of your ship. If you choose this way, you also get an extra weapon slot for your inventory and an installed Orokin Catalyst.
The second option is buying the Scindo Blueprint in the Market Console of your ship for 15.000 Credits. This means you have to craft it in the Foundry of your ship, having previously the required materials to do it, of course. Is not the quickest option, that’s obvious, but at least it is the most accessible one for all Tenno.