Maybye it is on the third Floor.
I think you have to find a special pokemon
in the solaceon ruins.
You can find the M form of Unown in the Solaceon Ruins of Pokemon Platinum. This form of Unown appears in the dead-end rooms of the Ruins.
salaceon town ruins where you find the unown
In Diamond it is in the ruins with the Unknown, I am not sure about Platinum though.
You find it in the solaceon ruins after you catch all the unown.
in the ruins east of solaceon town.
go to solcoan town and go into the ruins then wonder about and a wild unown (pokemon 114).
you can definitely find one in the solaceon town ruins and undergound
You will find Regirock at rock peak ruins route 228.
You can find it at Iceberg Ruins ( Mt. Coronet) Find information at Serebii!! I hope I helped!
You can't buy it. You have to find the HM in the game. It is located in the Solaceon Ruins