on island 3 in the berry forest
You can't catch it in the wild. You'll need to evolve it from Weepinbell with a Leaf Stone.
You can catch Chansey in Pokemon Crystal on Routes 13, 14, and 15.
bellsprout , wepinel,victribell , sandrew, sanslash , marill , azumarill , muk and remoraid
Get Leaf Green, or just catch a growlithe because Arcinine is by far the superior Pokemon.
trade it from leaf green
You have to catch a Bellsprout or a Weepinbell (Evolves from Bellsprout). Then you can use a Leaf Stone on the Weepinbell and it will become a Victreebel.
You can't catch it in the wild. You'll need to evolve it from Weepinbell with a Leaf Stone.
You cant catch magmar, magmortar, bellsprout, weepinbell, and victreebell. These are the pokemons you can catch in leaf green, but not in fire red: Sandshrew Sandslash Vulpix Ninetales Bellsprout Weepinbell Victreebel Slowpoke Slowbro Slowking Staryu Starmie Magby Magmar Pinsir Azurill Marill Azumarill Misdreavus Sneasel Remoraid Octillery Mantine Deoxys (defence form)
Gloom, Exeggcute, Weepinbell, and actually I think that's it since you can't catch Nuzleaf (or can you?).
The early routes.
dive 126_128 routes
routes 9 and 11
In Pokemon Leaf Green, you can catch Pokemon in the grass, water, or in a cave.
Routes 209 and 210 with the pokeradar.
You can catch Chansey in Pokemon Crystal on Routes 13, 14, and 15.
You can catch nincada mostly in the beginning of the game routes, and in petalburg woods.
You can catch wild Tauros on Routes 38 and 39 during the daytime.