This is an interesting one. The Korok weapons bonus allows you to reuse any material that breaks while attached. While this could be used for weapons, the obvious answer is to attach breakable materials to it. Chu Jellies, Elemental Fruits... but to me, the best option is easily the Gibdo Bone. It has 40 attack power, placing it on a level only matched by farmable Depths quest bosses, Silver and White Lynel Horns, and the Ancient Blade. It has a distinct downside however - unlike those materials, it BREAKS - very easily at that, due to its odd shape.

Now read the effect of this sword. Oh yeah. Its all coming together. Cheap and easy +40 attack, here we come.

And while you can attach breakable elemental objects to this, its not nearly as good - the Dragon parts, particularly the 16 power common-as-dirt Spike Shards, achieve the elemental effects without breaking and with a higher attack to boot, and can thus be attached to much better weapons. The fragile Gibdo bone, meanwhile, has to be constantly reattached to most weapons - except this one. Enjoy your 56 attack sharp stick!

As for finding one, well keep picking up the weapons beneath Korok Forest and they'll eventually become much more common. Look up a guide if you need more help finding these.