How to get the commander's medal? (seeking an answer)

I am a green hand. I'm stuck at level 43 of the heart tree.

I need more commanders' medals. I only have eight commanders now.

So, in addition to the recruitment form of the welfare center, The commander's medals that I have already won in the Heart Tree Store.

Is there any other way to get the commander's

Without buying in the game， Is there any other way to get the commander's medal?

Can you answer it for me?