Thunderblade and Great Thunderblade respawn areas
Solution 1:
The stalnox in Hickaly Woods drops a Thunderblade, and the one in the Hyrule Castle dungeon drops a Great Thunderblade.
Further reading:
- http://zelda.wikia.com/wiki/Thunderblade
- http://zelda.wikia.com/wiki/Great_Thunderblade
Solution 2:
Thunderblades can also respawn in the Coliseum, just north of the Great Plateau. See my answer about where to get frost blades. The same answer applies for Thunder Blades (+ spear) and fire weapons as well.