Cherrim - Surf south from Sangdem Town, there is a trainer on that route that has one.
Drifloon - Can be caught on Friday nights at Valley windworks.
Unown - Go to Solaceon Town, and go east to the Solaceon Ruins. Wild Unown can be found in there.
Riolu - Go to Canacalve City and take the Boat to Iron Island. You battle and walk around with a trainer there, like in Eterna Forest, and at the end, the trainer gives you an egg whioch hatches into Riolu. Alternatively, go to the Oreburgh Gate (West from Oreburgh City, you will need a Pokémon that knows Rock Smash, possibly strength and surf, and a Bike), and work your way downstairs. There is an Expert Trainer there (he looks like an old man) who has a Riolu as one of his Pokémon.
Hope I helped. :)
