True, bees have little food when there are no flowers. Remember they feed on nectar, which comes from flowers.
However, they can also get the same from fruits, such as oranges, pineapples and mangoes or sugar. This is why it is common to see bees buzzing over sugar bowls.
So, if you want to feed them, you should have cut fruits such as mangoes, pineapples and oranges nearby. Alternatively, build a hive that has a hole below through which bees can pass to access a container, filled with sweet fruits such as mangoes and oranges.
The bees will drop from the hive into the container to get food from the fruit. Also, remember that bees need water to create honey. Therefore, create some water nearby during the dry season.