You can only find it after you have deafeated the elite four and obtaind the national pokedex.
Go to route 228, and go to the part of it where there isa sort of blowing sandstorm, find the grassy areas and search around, it is not to hard to find, it will be at about level 53-Level 56.
Trade your rhydon while it is holding a "protecter".
In Pokémon Pearl, Rhydon evolves once you give it the Protector and trade it to another player.
A Protecter evolves Rhydon into Rhyperier.
A Protector, when traded with Rhydon, will evolve it into Rhyperior.
Trade A Rhydon While Holding PROTECTOR 99Lloyd99
You cannot get the protector to evolve Rhydon in Pokemon Red version, because Rhydon's ability to evolve with a protector into Rypherior is only available in the latest versions: Pokemon Diamond, Pearl, and Platinum. It is impossible to even get a protector in Pokemon Red version, let alone evolve Rhydon.
you cant evolve rhydon in fire red because the "protector" wasn't incorperated into the games until diamond/pearl
Rhydon, by having him holding the Protector and trade him he will evolve to Rhyperior
Trade it when it is holding a Protector. In Diamond and Pearl, this is found on Route 228.
you give it to a rhydon to hold and then trade it to a different game. it will evolve into a rhyperior.
I believe that Rhydon loves the Protector, but I only found that out by trading it with the Protector on
you can find a Rhydon on route 226 :)