You can search Pokemons you can be evolve without candy an item.
to search for trade evolutions pokemons just copy this :
this will give you all the pokemons that are eligible for Candy free evolotion after being traded to another Trainer.
pro tip :
if you want free fast xp in pokmeon go :
collect trade evolve pokemons and trade them in mass with a friend.
then evolve them all for free (no candies and no dust) in hours that give 3x xp for evolotions