Maps are found in large chests throughout each world or given to you by progressing the story. They are hard to miss generally, so you should have all maps by the time you complete the game with the following exceptions:
Firstly, Winnie the Pooh’s world and Atlantica both have one map you need to collect.
Secondly, the Cavern of Remembrance has several maps. These will likely be the last maps you collect as most of the cave is end game content. The cave initially unlocks right after the “1000 Heartless fight.”