Window part replacment

Hello!

I need to replace what I thiiiiiink is a broken balance in my window (it no longer stays up on it's own), but I'm having trouble finding the correct replacement part. The window itself is definitely older and I've attached a couple of photos, please let me know if you need any more information/pictures. One shot shows the balance on the left side, (and I've included a picture of the numbers on said balance) the other is the right side sans balance. Thank you!