You can't because you can only catch Oddish on Pokemon red version. the only way you can have Bellsprout on Pokemon red is trade from blue
Mostly in the Grasses, it's common, anywhere except Pallet town and Pewter City. (well some bellsprouts are in Pewter City.)
Bellsprout is only in leafgreen you must trade one to firered to have one.
Here are the grass pokemon in Red (not all of these are capturable): Bulbasaur, Bellsprout, Oddish, Tangela, Exeggcute.
you need to trade bellsprout, vulpix, and sanshrew from leafgreen and you can get the rest in fire red.
When you look in the PokeDex into the Bellsprout entry, it says: Area Unknown. That's because likely this Pokemon can not be caught in this version of the game. You might need to trade with Leaf Green.
bellsprout and what they evolve into
bellsprout, oddish.
You can't find a Vulpix in Pokemon FireRed version. That pokemon is version-exclusive to Pokemon LeafGreen.
in the toilet
You can't find Articuno in pokemondiamond but you can migrate it in pokemon leaf green version or pokemon fire red version.
Look for it in eBay or Amazon.
Pokemon only in Red - Ekans/Arbok, Oddish/Gloom/Vileplume, Mankey/Primeape, Growlithe/Arcanine, Scyther, and Electrabuzz Pokemon only in Blue - Sandshrew/Sandslash, Vulpix/Ninetales, Meowth/Persian, Bellsprout/Weepinbell/Victreebel, Magmar, Pinsir
You cant