Yakuza 3 Remastered

The coin lockers are located next to the confidence store in the southern part of Okinawa and next to the millennium tower in Komorocho. The keys will not start appearing until chapter 4. There are two types of keys to find, those you can run over and pick up naturally, and some you can find by going into first person mode and looking at the key. The keys are the bright flashing lights either on the ground or just out of normal reach. Obtaining 10 keys is real easy since there are two locations totaling 100 keys to find. You can open 10 lockers in either city at once or a combination if you are casually playing.
https://gamefaqs.gamespot.com/ps4/239455-yakuza-3-remastered...
CyricZ has a good guide for all of the keys for anyone looking for the cheat items from the lockers.