On victory road you find wild Rhydon at about level 40. I don't remember where to find a trainer with one, but you could also battle a friend with one in the union room.
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!!
i can't remember what trainer has a ryhdon but if you go to victory road there are some
bertha has a rhypheorior and rhydons are only wild at lv53
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.
on victory road
Trainer on route 212
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.
Rhydon evolves when the "Protector" is held and the Pokemon is traded.
trainer on victory road
you do not need one you can find them on VictoryRoad [wild]
In DP no In Platinum, Route 217 (Trainer)
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.