Aluminum window- round balance holder

I'm afraid that we don't have a replacement for this part. We do have the 55-063 nylon window stop, which is used for a 5/8" tube balance and fits in a 1-1/4" wide track. That may work, but I'm not certain. 

If not, and if you're handy, you can go to your local hardware store, purchase an aluminum channel, and then cut and drill a hole for the screw.