You can, however, obtain a Thunderstone in the following ways:
* Route 224 (Diamond/Pearl) or Route 226 (Platinum): This route has a chance to contain a Thunderstone, making it a possible location to find one.
* Trading: Other players may be willing to trade a Thunderstone with you.
* Pokémon Ranger: You can obtain a Thunderstone in the Pokémon Ranger games and transfer it to Diamond/Pearl/Platinum via the Pal Park.
It's worth noting that the Solaceon Ruins are not known for having a Thunderstone, so you're unlikely to find one there.