Pokemon can evolve by reaching a certain level, becoming good friends with their trainers,
and many other ways.
Some Pokemon evolve by the use of an item. I'll list them here.
 Deep Sea Tooth: 
   
- Have a Clamperl hold this item and trade it. The Clamperl will evolve into a Huntail.
- Found on Route 20 [Dowsing Machine] and may be held by wild Sharpedo and Carvanha.
~ Carvanha is found in the Pokewalker. The course is Warm Beach.
~ Sharpedo can't be caught in the Pokewalker or in the wild in this game so...
 Dragon Scale: 
   
- Makes a Seadra holding this item evolve into Kingdra when traded.
- Found at Pokeathlon Dome as a prize, Mt. Mortar, and wild Horsea, Seadra, Dratini, and
Dragonair may hold them.
~ Seadra & Horsea are found at the Sea Foam and Whirl Islands.
~ Dragonair can be found at the Dragon's Den.
~ Dratini can be found in the Safari Zone and the Dragon's Den.
 Dubious Disc: 
   
- Makes a Porygon 2 holding this item evolve into Porygon Z when traded.
- It is found on Route 42
 Electirizer: 
   
- Makes an Electabuzz holding this item evolve into an Electivire when traded.
- It is found in Cerulean Cave.
 King's Rock: 
   
- Makes a Poliwhirl holding this item evolve into a Politoad.
- Makes a Slowpoke holding this item evolve into a Slowking.
- It can be found at the Slowpoke Well, the Pokeathlon Dome, and wild Slowbro and
Poliwhirl may be found holding this item.
~ Poliwhirl can be found on Routes 22, 28, 30, 31, and 44, Ecruteak City, Mt. Silver,
Violet City, Viridian City, and Cerulean Cave.
~ Slowbro can be foundcat the Slowpoke Well, Safari Zone and Seafoam Islands.
 Magmarizer: 
   
- Makes a Magmar holding this item evolve into a Magmortar when traded.
- It is found at Cinnabar Island.
 Metal Coat: 
   
- Makes an Onix holding this item evolve into a Steelix when traded.
- Makes a Scyther holding this item evolve into a Scizor when traded.
- It can be found at the S.S. Aqua, the Pokathlon Dome, and wild Magnemite may hold this
item.
~ Magnemite can be found at Routes 6, 11, 38, 39, and the Safari Zone.
 Oval Stone: 
   
- Makes Happiny evolve into a Chansey when leveled up during the day [holding the item]
- Can be found in the Rock Tunnel and wild Chansey may be olding it.
~ Chansey may be found at Routes 13, 14, and 15.
 Protector: 
   
- Makes a Rhydon holding this item evolve into a Rhyperior when traded.
- Can be found at Mt. Mortar.
 Razor Claw: 
   
- When held, causes Sneasel to evolve into Weavile while leveled up during the night
- Can be found at the Battle Frontier [48 BP]
 Razor Fang: 
   
- When held, causes Gligar to evolve into Gliscor while leveled up during the night
- Can be found at the Battle Frontier [48 BP]
 Reaper Cloth: 
   
- Causes a Dusclop holding this item to evolve into Dusknoir when traded
- Can be found at Silver Cave, Winner's Path [Pokewalker], and held by wild Duskull
~ Duskull can be found at the Safari Zone [refer to other cheats]
 Upgrade: 
   
- Causes a Porygon2 holding this item to evolve into Porgon-Z when traded
- Can be found at the Silph Co. in Saffron City
 Fire Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Vulpix ---> Ninetales
Growlithe ---> Arcanine
Eevee ---> Flareon
- Can be obtain from|at Bill's grandfather, Schoolboy Alan (Route 36), Bug-Catching
Contest, Pokeathlon Dome, Warm Beach [Pokewalker]
 Water Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Poliwhirl ---> Poliwrath
Shellder ---> Cloyster
Staryu ---> Starmie
Eevee ---> Vaporeon
Lombre ---> Ludicolo
- It can be obtained from|at Bill's grandfather, Fisher Tully (Route 42), Bug-Catching
Contest, Seafoam Islands, Pokeathlon Dome
 Thunderstone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Pikachu ---> Raichu
Eevee ---> Jolteon
- This item can be obtained from|at Bill's grandfather, Lass Dana (Route 38), Bug-Catching
Contest First Prize, Pokeathlon Dome
 Leafstone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Gloom ---> Vileplume
Weepinbell ---> Victreebel
Exeggcute ---> Exeggutor
Nuzleaf ---> Shiftry
- It can be obtained from|at Viridian Forest, Bill's grandfather, Picnicker Gina (Route
34), Bug-Catching Contest First Prize, Pokeathlon Dome
 Moon Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Nidorina ---> Nidoqueen
Nidorino ---> Nidoking
Clefairy ---> Clefable
Jigglypuff ---> Wigglytuff
Skitty ---> Delcatty.
- It can be obtained from|at Tohjo Falls, Ruins of Alph, Mom, Bug-Catching Contest First
Prize, Mt. Moon Square [Monday], Pokeathlon Dome
 Sun Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Gloom ---> Bellossom
Sunkern ---> Sunflora
- It can be obtained from|at Bug-Catching Contest First Prize, Pokeathlon Dome
 Shiny Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Togetic ---> Togekiss
Roselia ---> Roserade
- It can be obtained from|at Pokeathlon Dome, National Park, Bird Keeper Josh
 Dusk Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Murkrow ---> Honchkrow
Misdreavus ---> Mismagius
- It can be obtained at the Pokeathlon Dome and Bug-Catching Contest
 Dawn Stone: 
   
~ Use this item on the following Pokemon to make them evolve ~
Male Kirlia ---> Gallade
Female Snorunt ---> Froslass
- Can be obtained at Pokeathlon Dome and Mt. Silver
 Oval Stone: 
   
- If held, causes Happiny to evolve into Chansey when leveled up during the day
- It can be obtained from wild Chansey.
~ Chansey can be found on Routes 13, 14, and 15
 Notes: 
- When trying to get items from the Pokeathlon Dome, please note that the items appear on
certain days. Want to know when you can find the item LOOK IT UP! If you can't find it [I
doubt it], use one of the sites I give you in the following or ask me myself
- Need to find a trainer Do the same as the above!
 Websites: 
- Seribii.net
- Bulbapedia