In Keras how to get the `class_indices` or prediction labels for an existing model
Don't know if you solved already.
I faced this problem yesterday, and the only solution that came to my mind is saving a dictionary to a numpy file after a train_generator is set; something like:

np.save('FILENAME', self.train_generator.class_indices)


when you finish your training. 
Then, when you do your single prediction:

single_pred = np.squeeze(self.model.predict(image))

if isfile('FILENAME.npy'):
    class_indices = np.load(self.indices_file + '.npy').item()

results_dict = dict(zip(class_indices.keys(), single_pred))