I am assuming the only way to get this schematic is through one of the mission skills. I have been running the underworld missions for level 25-32, since the belt is 27, for what feels like an eternity. I wanted to see if anyone out there had any other advice on how to get this schematic. I have been searching the GTN as well in case someone is selling it.

 

I believe it requires a critical hit on the mission and that the reward for that crit is also random so the odds are stacked against me. But was curious as to what others thought or may have experience.

I have it on one of my characters and I got it through the GTN. It is there but it is RNG. The only way to get it is to keep doing what you're doing; running missions and checking the GTN.