I don't think you can find rhydon itself, I think you have to find a ryhorn, which can be found at victory road, about level 45, or somewhere around there (forgot what level exactly) and it evolves into rhydon at level 49, but, (from another answer I heard (not wanting to take credit for it)) wait till it gets to level 55 first so give it everstone to stop it evolving because it learns earthquake at 55 where rhydon learns it a 65. Earthquake is the best ground move in the game.
The evolved form of Rhyhorn is Rhydon
You can encounter a Rhydon on Victory Road on the first floor. A trainer on victory road will also have a Rhydon in his party.
You have to trade it while holding a proctector item.
You can catch it in the Resort Area. PS: It appears at differents times. So be on the lookout!
You need to evolve Rhydon. Rhydon evolves when you trade it when it holds a Protector. You find a Protector on Iron Island and Route 228. See related link on details on where to find Rhydon.
there aren't any trainers who use a Rhydon in Pokemon platinum, but you can see a Rhydon on Route 228 ~ actually there is a trainer in Pokemon platinum who has a Rhydon and he is in victory road. when you are in victory road where you see all the water just go surf on the first one and then land where you see three lakes. once you are there go all the way right and you should see a trainer jogging up and down beside an item. battle him and he has a Rhydon in his party.~ How would people get to route 228 IF THEY WANTED TO FINISH THEIR SINNOH POKEDEX!!
Rhydon evolves when the "Protector" is held and the Pokemon is traded.
When looking at the item, it does say "a Pokemon loves this item". It is a hint to give a Pokemon that item. Well that Pokemon is a rhydon. Give a rhydon that item to hold. Trade it and see what happens...
Trade it with the Protector on it
At M.T Stark
You have to get the Moon stone.
to evolve rhydon you need a protector. I think you can get one on stark mountain. Then you have to give it to Rhydon and trade with a friend.
you can find one in victory road.
You cannot find rhypierier on Pokemon Platinum. You have to trade rhydon while it's holding the protector.
The evolved form of Rhyhorn is Rhydon
Trade Rhydon while it holds this to get a Rhyperior
on victory road