Go to the contest hall in lilycove and talk to the lady on the left. She would give you a poke block case.
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You can get it in Verdanturf city in the Pokemon contest.
The Poke Radar is not available in Pokemon Sapphire. The Poke Radar is an item exclusive to Pokemon Diamond, Pearl, Platinum, X and Y.
I don't know about ruby or sapphire as i don't have them, but i do know in emerald you get the pokeblock case in Lilycove by talking to one of the ladies behind the counter in the contest hall.
There is a limit to how many PokeBlocks a certain Pokemon can eat before you can't give it any more, so use PokeBlocks wisely.
use a ultra/great ball