Finding Pokemon (Platinum)

Turtwig: Route 201 Event / Rival
Grotle: Evolve Turtwig / Rival
Torterra: Evolve Grotle / Rival
Chimchar: Route 201 Event / Rival
Monferno: Evolve Chimchar / Rival
Infernape: Evolve Monferno / Rival
Piplup: Route 201 Event / Rival
Prinplup: Evolve Piplup / Rival
Empoleon: Evolve Prinplup
Starly: Route 201
Staravia: Rival
Staraptor: Rival
Bidoof: Route 201
Bibarel: Route 208 / Route 209
Kricketot: Route 202 Trainer
Kricketune: Route 215
Shinx: Route 202
Luxio: Route 207
Luxray: Leader Volkner
Abra: Eterna Forest Trainer
Kadabra: Galactic Admin Saturn
Alakazam: Elite Four Lucian
Magikarp: Old Rod
Gyarados: Leader Crasher Wake
Budew: Route 204
Roselia: Eterna Gym
Roserade: Leader Gardenia
Zubat: Ragged Path
Golbat: Iron Island
Crobat: Galactic Leader Cyrus
Geodude: Ragged Path
Graveler: Iron Island
Golem: Elite Four Bertha
Onix: Leader Roark
Steelix: Leader Byron
Cranidos: Leader Roark
Rampardos: Victory Road
Shieldon: Route 215 Trainer
Bastiodon: Leader Byron
Machop: Route 207
Machoke: Leader Maylene
Machamp: Victory Road
Psyduck: Oreburgh Gate
Golduck: Pastoria Gym
Burmy: Route 202 Trainer
Wormadam: Route 214 Trainer
Mothim: Route 210 North Trainer
Wurmple: Eterna Forest Trainer
Silcoon: Eterna Forest Trainer
Beautifly: Eterna Forest Trainer
Cascoon: Eterna Forest Trainer
Dustox: Eterna Forest Trainer
Combee: Route 208 Trainer
Vespiquen: Elite Four Aaron
Pachirisu: Valley Windworks
Buizel: Valley Windworks
Floatzel: Leader Crasher Wake
Cherubi: Eterna Gym
Cherrim: Leader Gardenia
Shellos: Valley Windworks
Gastrodon: Route 218
Heracross: Elite Four Aaron
Aipom: Route 205 Trainer
Ambipom: Route 216 Trainer
Drifloon: Valley Windworks Friday Night
Drifblim: Leader Fantina
Buneary: Eterna Forest
Lopunny: Route 216 Trainer
Gastly: Old Chateau
Haunter: Hearthome Gym
Gengar: Victory Road
Misdreavus: Lost Tower
Mismagius: Leader Fantina
Murkrow: Galactic Leader Cyrus
Honchkrow: Galactic Leader Cyrus
Glameow: Galactic Grunts
Purugly: Galactic Admin Mars
Goldeen: Route 205 Trainer
Seaking: Route 217 (north tree corridor)
Barboach: Route 212 South Trainer (Fisherman)
Whiscash: Elite Four Bertha
Chingling: Victory Road Trainer
Chimecho: Victory Road Trainer
Stunky: Galactic Grunts
Skuntank: Galactic Admin Jupiter
Meditite: Leader Maylene
Medicham: Iron Island (Trainer)
Bronzor: Route 207 Trainer
Bronzong: Elite Four Lucian
Ponyta: Route 207
Rapidash: Elite Four Flint
Bonsly: Route 208
Sudowoodo: Route 216
Mime Jr.: Route 208
Mr. Mime: Elite Four Lucian
Happiny: Route 210 South Trainer
Chansey: Route 210
Blissey: Victory Road Trainer
Cleffa: Mt. Coronet
Clefairy: Mt. Coronet
Clefable: Victory Road
Chatot: Route 212 North Trainer
Pichu: Route 209
Pikachu: Route 206 (Cycling Road)
Raichu: Leader Volkner
Hoothoot: Route 212 South Trainer
Noctowl: Route 210 North
Spiritomb: Champion Cynthia
Gible: Victory Road Trainer
Gabite: Victory Road Trainer
Garchomp: Champion Cynthia
Munchlax: Rival
Snorlax: Rival
Unown: Solaceon Ruins
Riolu: Iron Island (Egg Event)
Lucario: Leader Maylene
Wooper: Route 212 South
Quagsire: Leader Crasher Wake
Wingull: Route 222 Trainer
Pelipper: Route 223
Girafarig: Valour Lakefront
Hippopotas: Route 216 Trainer
Hippowdon: Elite Four Bertha
Azurill: Pastoria Gym
Marill: Pastoria Gym
Azumarill: Pastoria Gym
Skorupi: Route 210 North
Drapion: Elite Four Aaron
Croagunk: Galactic Grunts
Toxicroak: Galactic Admin Saturn
Carnivine: Route 214 Trainer
Remoraid: Route 222
Octillery: Route 223 Trainer
Finneon: Route 222 Trainer
Lumineon: Route 223 Trainer
Tentacool: Route 218
Tentacruel: Route 223
Feebas: Route 222 Trainer
Milotic: Champion Cynthia
Mantyke: Route 218 Trainer
Mantine: Route 223 Trainer
Snover: Route 216 / Route 217
Abomasnow: Leader Candice
Sneasel: Leader Candice, Galactic Admin Cyrus
Weavile: Galactic Admin Cyrus
Uxie: Lake Acuity Cavern
Mesprit: Lake Verity Cavern
Azelf: Lake Valour Cavern
Dialga: Atop Spear Pillar [Event]
Palkia: Atop Spear Pillar [Event]
Manaphy: Pokemon Mansion on Route 212 (book)
Rotom: Old Chateau
Gligar: Route 207 Trainer
Gliscor: Elite Four Bertha
Nosepass: Route 207 Trainer
Probopass: Route 210 North
Ralts: Route 209
Kirlia: Route 217
Gardevoir: Victory Road Trainer
Gallade: Elite Four Lucian
Lickitung: Route 215
Lickilicky: Victory Road
Eevee: Hearthome City (Bebe)
Vaporeon: Route 214 Trainer
Jolteon: Leader Volkner
Flareon: Route 214 Trainer
Espeon: Elite Four Lucian
Umbreon: Route 212 South Trainer
Leafeon: Route 212 South Trainer
Glaceon: Route 217
Swablu: Route 210 North
Altaria: Victory Road
Togepi: Eterna City (Egg)
Togetic: Victory Road
Togekiss: Champion Cynthia
Houndour: Route 214
Houndoom: Elite Four Flint
Magnemite: Fuego Ironworks
Magneton: Leader Byron
Magnezone: Victory Road
Tangela: Route 210 North
Tangrowth: Victory Road
Yanma: Route 214
Yanmega: Elite Four Aaron
Tropius: Route 214
Rhyhorn: Route 214
Rhydon: Victory Road
Rhyperior: Elite Four Bertha
Duskull: Leader Fantina
Dusclops: Route 216
Dusknoir: Victory Road
Porygon: Route 214 (Collector)
Porygon2: Route 216
Porygon-Z: Victory Road
Scyther: Route 210 North
Scizor: Elite Four Aaron
Elekid: Route 210 South
Electabuzz: Sunyshore Gym
Electivire: Leader Volkner
Magby: Route 210 South
Magmar: Route 217
Magmortar: Elite Four Flint
Swinub: Route 216
Piloswine: Route 217
Mamoswine: Victory Road
Snorunt: Acuity Lakefront
Glalie: Snowpoint Gym, Victory Road
Froslass: Leader Candice
Absol: Victory Road
Giratina: Distortion World
~~~~~~
As you can see, it's mostly about finding which trainer has it. Giratina's an exception, of course. If you have any questions or want to correct something, please PM me.