Guard at the end of metal balance

The part you are referring to is known as a top sash guide. We can help you locate a replacement. You will need to remove it from the window completely and send us a photo of it for us to review. I notice you mentioned having two of the guides at the bottom of the window. Usually only one is installed. Could you remove the additional piece you are referring to so we can take a closer look for you?

Ah, I see. From your photos, it looks like you need a custom made balance. We can make it, but it will have to be a special order. Your pictures are very helpful and have told us a lot. Can you  just tell me the stamp printed on the metal channel? Can you also tell me how many you need? 

Your original post also mentioned a top sash guide, but I'm still not sure what yours would be. We'd have to see the original in order to identify it.