Is there a way to find out where mailboxes are located?

There's two main places.

On the outside areas of the area. Usually, there's two types, a single box or stacked boxes. Single boxes are the ones with a flag that indicates to mailmen that a letter needs going out. Stacked is a group of mailboxes stacked together in one area where a mailman can go to send mail to groups of houses at once. Stacked are usually for apartments, and single are usually for individual houses.

Mailboxes could also be located on the inside of apartments. They are usually hang on the first floor on the apartment building where the mailman goes into to send mail. These follow the rules of stacked types.