While most Pokemon can evolve only using candy, some require an evolve item as well. Evolve items are unlocked at level 10 and you will start to see them drop from PokéStops rarely.

Image Item Description Evolve from/to
Dragon Scale A scale that can make certain species of Pokemon evolve. It is very tough and inflexible. Seadra to Kingdra
King’s Rock A rock that can make certain species of Pokemon evolve. It looks like a crown. Poliwhirl to Politoad

Slowpoke to Slowking

Metal Coat A coating that can make certain species of Pokemon evolve. It is a special metallic film. Onix to Steelix

Scyther to Scizor

Sun Stone A peculiar stone that can make certain species of Pokemon evolve. It burns as red as the evening sun. Gloom to Bellossom

Sunflora

Up-Grade A transparent device that can make certain species of Pokemon evolve. It was produced by Silph Co. Porygon to Porygon2