Where can i find these please and thank you :3

Thunder stones drop from mobs, kind of rare. Piercing stones are the same, but you can also get them from disassembling magatamas you don't need with Kaguya.

Wow thanks but it must be really rare i haven't seen any thunder ones drop D:

yeah it's really rare items, but i got many of them...
1pcs piercing stone.
1pcs cutting stone.
1pcs dark stone.
1pcs light stone.
1pcs thunder stone.
2pcs inferno stone.
2pcs miracle stone.