Some of the moddable weapons can be learned by the trainer, while others can be learned from schematics (obtained through Treasure Hunting and Investigation).
Treasure Hunting missions have a chance to yield Custom (orange) lightsaber schematics as a reward. Investigation missions have a chance of yielding Custom (orange) tech weapon schematics as a reward.
Here is a list of all crafted moddable weapons for both Artifice and Armstech. For the 3D models (ranged weapons only, since the lightsabers are..well..a handle with a color crystal ), go to the next page.
You can check the looks of ranged weapons on the next page..