Head west of Celadon to the cycling road, from there go to Fuschia city to battle Koga.
You get it at wayyard cave below the cycling road.
The 'Cycling Road' is between Eterna and Oreburgh (it doesn't go directly to Oreburgh, but that is the nearest city).
fight and ride!
its all in the timing
wake the snorlax at the top of cycling road with the pokeflute then down cycling road to fuschia
Cycling Road can be found on Route 17 (East of Fuschia and Celadon).
Gligar is in the grass near cycling road if you insert Pokemon Emerald. In Platinum, the dongle feature is not nessecary.
take cycling road from Fuchsia city
You get it from Dawn(or brandon) at the end of cycling road
in wayward cave by the cycling road thingy
its where you cycle on your bike and battle trainors