Here are some Pokemon you *can* find in FireRed:
* Normal Type: Pidgey, Rattata, Spearow, Zubat, Meowth, Ekans, Mankey, Growlithe, Abra, Machop, Bellsprout, Oddish, Ponyta, Farfetch'd, Dratini, Lickitung, Chansey, Ditto, Snorlax, Hitmonlee, Hitmonchan, Scyther, Jynx, Mr. Mime, Tauros, Lapras, Eevee
* Fighting Type: Mankey, Machop, Hitmonlee, Hitmonchan
* Flying Type: Pidgey, Spearow, Zubat, Doduo, Dodrio, Fearow, Pidgeotto, Farfetch'd
* Poison Type: Ekans, Koffing, Weezing, Venonat, Venomoth, Grimer, Muk, Nidoran (F), Nidorina, Nidoqueen, Nidoran (M), Nidorino, Nidoking
* Ground Type: Diglett, Dugtrio, Sandshrew, Sandslash
* Rock Type: Geodude, Graveler, Golem, Onix
* Bug Type: Caterpie, Metapod, Butterfree, Weedle, Kakuna, Beedrill, Scyther
* Ghost Type: Gastly, Haunter, Gengar
* Steel Type: (Not in FireRed)
* Fire Type: Charmander, Charmeleon, Charizard, Vulpix, Ninetails, Growlithe, Arcanine, Ponyta, Rapidash
* Water Type: Squirtle, Wartortle, Blastoise, Psyduck, Golduck, Poliwag, Poliwhirl, Poliwrath, Tentacool, Tentacruel, Shellder, Cloyster, Horsea, Seadra, Kingler, Lapras
* Grass Type: Bulbasaur, Ivysaur, Venusaur, Oddish, Gloom, Vileplume, Bellsprout, Weepinbell, Victreebel
* Electric Type: Pikachu, Raichu, Pichu, Magnemite, Magneton, Voltorb, Electrode
* Psychic Type: Abra, Kadabra, Alakazam, Drowzee, Hypno, Mr. Mime, Jynx
* Ice Type: (Not in FireRed)
* Dragon Type: Dratini, Dragonair, Dragonite
* Dark Type: (Not in FireRed)
* Fairy Type: (Not in FireRed)
You can find Skitty in later games like Pokemon Ruby and Sapphire, Pokemon Diamond and Pearl, and Pokemon Black and White.