You cannot. You can only do so in Pokemon HeartGold and SoulSilver.
...you beat the gym leaders
You have to beat the challenge a certain amount of times.
It is on Mossdeep City. There are Twin Gym leaders
after you beat 4 to 5 gym leaders you can face him
you can only rebattle gym leaders when you have defeated the elite four, check your match call on the pokenav when you have
Water.
...you beat the gym leaders
No. But, you can fight them (as gym leaders) In Pokemon Silver/Gold.
There are gym leaders in almost every city and there are lots of different Pokemon and trainers in the gyms.
beat all battle frontier leaders
No, this feature is only available in Pokemon Emerald.
Defeat all of the Gym leaders on Emerald. ~KKMG1
You have to beat the challenge a certain amount of times.
It is on Mossdeep City. There are Twin Gym leaders
The Leaders Pokemon are level 100 as well as the Pokemon you are given In the battle frontier (Ruby,Emerald,Saphire)
after you beat 4 to 5 gym leaders you can face him
you can only rebattle gym leaders when you have defeated the elite four, check your match call on the pokenav when you have