The village level determines which cards can be found in chests as well as their rarity.
The cards are spread throughout all the villages in the game, so if you notice that you are no longer finding any new cards, it's a good indication that it's time to move up a few villages before continuing your search. Please note that not all players will find the same cards in exactly the same places.
However, make sure you buy enough chests to find all the cards as you don't want to leave any behind. Always note that Gold cards are in higher villages than you will find the rest of the cards.