Throughout the Story of Mafia, there are 172 collectibles. Most of these collectibles can be obtained during Free Roam, however, there are certain collectibles which are missable during story chapters.
I first found one of the Gangster Monthly in Chapter 8 during the hotel.
I suggest using the following guide to help you find all collectibles -
https://www.powerpyx.com/mafia-1-remake-definitive-edition-c...