The third Gym is the Gym in Veilstone City. You can get there by looking on your map. The leader specializes in Fighting Pokemon.
if you are looking for the third gym badge i suggest Veilstone city.
it's the 3rd badge!
The third badge is in Goldenrod City.
You get your 3rd badge in Veilstone city against Maylene.
I have Pokemon platinum the 3rd gym leader always their your probaly just not lucky.
Defeat the 3rd Gym Leader, Wattson, in Mauville City.
You can get a badge and TM Shadow Claw after beating the third available gym leader, which is Fantina with the Relic Badge. (She uses Ghost types)
The city in Pokémon X in which features the third Badge is Shalour City. The Gym Leader is named Korrina and she is a Fighting-type specialist.
Celadon city, use the town map to aid you on the way there.
The 3rd gyms badge will grant you the ability to use Fly outside of battle, the 3rd gym is in vermilion city.
you got to go to veilstone and that's where she is.
Platinum