You will get the Dowsing MCHN from Bianca after you defeat Gym Leader Lenora in Nacrene City. Bianca will greet you once you exit the Gym.
But before you’re able to challenge the Nacrene City Gym, you’ll need to obtain your first Gym badge in Striaton City.
The Dowsing MCHN is Black/White’s version of the Itemfinder, and it’s the easiest way to find hidden items scattered across Unova.
Getting the Dowsing MCHN
Step 1: After defeating Lenora at the Nacrene City Gym, exit the building.
Step 2: Upon exiting the Gym, Bianca will give you the Dowsing MCHN, which is a gift from Fennel.
How To Use the Dowsing MCHN
The Dowsing MCHN is essentially a radar that allows you to find hidden items across Unova. It is designed to stay alert as you journey from city-to-city, and it can even be used simultaneously with the Bicycle. This makes it much easier to cover ground faster.
This key item is easy to use too:
As you travel around, the radar will begin flashing an arrow in the direction of the closest hidden item.
Following that direction will lead you to the item’s exact location.
If you’re standing on the tile containing the hidden item, the screen will change and four arrows will appear.
Simply move one tile over and press A to grab the hidden item.
You can access the Dowsing MCHN from the Key Items pocket in your bag, and it’s an ideal device to hotkey for easy access if you’re planning to hunt for hidden overworld items.