Go to the battle subway located in Nimbasa City,
There is a train with a tanish color, That is the train to take you to Anville Town.
After arriving in Anville Town there is a house located East of the entrance and
towards the bottom. That is the Lost & Found House,
A Depot Agent handing out lost-and-found items lives in the south-eastern house, initially giving the player a Rare Candy. When visited, he will give a vitamin, Max Revive, or Max Elixir for each set of seven consecutive battles won at the Battle Subway since last visit, capping at ten.
He will give Items throughout your Journey, If you stop by there.
There is still more to do.
Every Saturday and Sunday, except on days when the Worker talks about the Hyperspeed Train, traders are present in town, who ask to trade their items for items in the player's bag.
As Bulbapedia Said,
There is people who will wan't to trade items.
That Is About All You Can Do,
Anville Town only has two main things.
There is a Ultra Ball In light grass at the north of the town
(Hidden, So use Dowsing Machine.)
And: There is a rare candy you can get, From a man in the house at
the southeast of the town.
Hope I Helped! :D