Swordsman Archive
Thread: Sword Core
Sword cores are lootable in the Genosian Cave on Yavin 4. From that cave, you can loot sword cores, reinfocement cores (usable for Powerhammers and non-sword weapons), Power Cubes (Green, Red, Yellow, or White), Schematics for Sword or Reinforcement cores, two new weapons (Genosian Sonic Blaster, a stun damage pistol, and the Disrupter Rifle, acid damage). You can also get the schematic for the rifle there from an NPC quest. There are other things lootable in the cave, but those are the main things you will be looking for.
Regarding the power cubes, these are used to enhance various weapons. The yellow boosts damage, the green boost durability, and the red reduce HAM costs (and encubrances). The white, I believe, do not enhance anything, but can be used as place holders to build the weapon if you do not have the resources that fit in that part of the schematic. I know they are needed for the Disrupter rifle, but I do not know about the Scythe.
If you can get the schematics for the sword core, your weaponsmith may be able to make you a better scythe using cores from teh schematic rather than the looted ones. Often crafted components can be built to exceed looted ones.