This can be farmed in an are just after the antenna room. You will jump down to a room with a barrel to your right. There will be a few suits of armor in this area. Take the barrel and throw it at one of the enemies, they will go through a stun animation. Restart the checkpoint and do this over and over.
Here is a video guide with English commentary!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdULD7WVqUHgB...