Must evolve it or trade it.
You can't find garchomp or its previous evolutions in the game. You can see a garchomp if you battle cynthia.
What you do is, you got to any Pokemon center. Got to the second floor and trade with a friend that has it in diamond, pearl, or platinum.
A rare Pokemon to get in Wayward Cave and totally worth while in my opinion is Gible. Gible is the 'baby' version of Garchomp.
pokemon heart gold
Can get one, in emerald its a fourth gen pokemon.
You can't. You need to evolve Gabite.
You can find Red at Mt.Silver at the top. But be warned he is tough.
You can see Garchomp when you battle the Pokemon League Champion, Cynthia. You can find Gible on the B1F of Wayward Cave.
garchomp in hippowdon temple
find the ice path and follow it
i dont think there is mewthree
in Pokemon ranger 2 i would say darkrai/heatran/garchomp/or charizard.