This guide will let you know how you can get Gauss in Warframe.
The Gauss parts can drop from a specific reward pool of a particular disruption mission node, and you can buy his primary blueprint from the store with credits.
The specific node you’re going to be running is Kappa, on sedna, and you have to get C rotations every round. You can get it on rounds 3 and every round after that.
In round 3, you will need to defend all four conduits. And then defend three conduits in every round after that to get the rotation rewards.
While the parts don’t have the lowest drop rates out of the items in its reward pool, it probably will still take you some time before you get all three gauss components/parts.