I appreciate you wanting to use a face mask to prevent spreading your flu and that's exactly what WHO advised; masks should be used by those who are infected and by health workers; sadly all masks have been hoarded.
If you are unable to find any masks, if you want something better than a hanky, as a last resort you can try DIY face mask such as this one - https://www.youtube.com/watch?v=WLTmrnRHQkk.