First, go to seven island. Then, go to the end of the seven island. (before go on surf)
There will be two Cooltrainer (one boy and one girl) they each are having all 5 pokemons together. Use vs seeker agian and agian.

At the last, the boy want will have a rhydon, a slowbro, an unsaring, a kangaskhan, a machcamp.

The girl one will have a persian, a dewgong, a ninetales, a rapidash, a girafil. (I forgot how to spell)

Their all are about 52 till 54 level.

If your pokemon is hurt badly, go inside the house and join the chansey dance and it recover your pokemon.

Hope this help.