I believe this to be a massive list, however I currently have this small list of useful items.
Light Ball - Red's Pikachu
Lum Berry - Lance's Salamence
Wacan Berry - Clair's Gyrados
Leftovers - Wild Snorlax
Iron Ball - Blue's Machamp
Black Sludge - Koga's Muk
Leftovers - Koga's Swalot
Sitrus Berry - Bugsy's Scyther
Lum Berry - Whitney's Miltank
Sitrus Berry - Morty's Gengar
Sitrus Berry - Chuck's Poliwrath
Sitrus Berry - Jasmine's Steelix
Sitrus Berry - Pryce's Piloswine
Sitrus Berry - Claire's Kingdra
Sitrus Berry - Will's Xatu
Sitrus Berry - Koga's Crobat
Sitrus Berry - Bruno's Machamp
Sitrus Berry - Karen's Houndoom
Sitrus Berry - Lance's Dragonite
Sitrus Berry - Lt. Surge's Electabuzz
Sitrus Berry - Sabrina's Alakazam
Sitrus Berry - Erika's Bellossom
Black Sludge - Biker Dale's Gulpin (Route 17)
Sitrus Berry - Janine's Venomoth
Chesto Berry - School Kid Connor's Zigzagoon (Route 14)
Sitrus Berry - Teacher Clarice's Zigzagoon (Route 14)
Toxic Orb - Super Nerd Sam's Muk (Route 8)
Sitrus Berry - School Kid Dudley's Oddish (Route 25)
Sitrus Berry - School Kid Joe's Tangela (Route 25)
Sitrus Berry - Lass Laura's Gloom (Route 25)
Sitrus Berry - Misty's Starmie
Sitrus Berry - Brock's Onix
Sitrus Berry - Camper Pedro's (oh god) Linoone (Route 20)
White Herb - All of Blaine's Pokemon
Sitrus Berry - Blue's Pidgeot
EDIT 1: Battle Frontier trainers are here. The list is massive, click on the trainer to see each Pokemon and it's item. It's seriously a lot of Pokémon and trainers.
EDIT 2: No other Johto trainer has any Pokemon that that any items, I literally looked at EVERY TRAINER. Kanto to come in the morning.
All done.
Hope I helped!
