Window balancer (?)

I'm afraid we can't replace the plastic pulley of a channel balance. You won't find any company who does. If that has broken then you need an all new balance.

We can help, but we will need more detailed pictures. Please show me the top and bottom of the balance, as well as the stamp printed on it. If you have an undamaged balance to use for these photos, that would be a huge help. 

We may have more questions after that, but these will at least give us a good place to start. Thank you!