Where are the NPC Pokemon traders in Pokemon Sun & Moon and which Pokemon do they offer?

From this site, this is a list of all of the in-game trades you can make in Sun & Moon:

Player Lillipup for NPC Bounsweet (Called Bouncee)

• In the Pokémon Center before the Lana's Trial (Route 5, near Brooklet Hill)

Player Zubat for NPC Poliwhirl (Called Whirly)

• In the Pokémon Center in Konikoni City.

Player Pancham for NPC Happiny (Called Happini)

• In the Sushi High Roller in Maile City.

Player Haunter for NPC Graveler

• In the Pokémon Center closest to the Aether House.

Player Granbull for NPC Steenee (Called Stena)

• In Seafolk Village, on the docks.

Player Bewear for NPC Talonflame (Called Talo)

• Just before the entrance to the Battle Tree in Poni Gauntlet.

Player Spearow for NPC Machop Nickname: Macho
Ability: No Guard
Nature: Brave
Held Item: X Attack

• In the Pokémon Center on Route 2.

_{(Locations provided from Serebii)}