Looking for channel balance window top plastic

Hello, Santhosh. This part is called a top sash guide. Your exact model isn't made anymore, but our 18-171 can work as an alternative with a little handiwork. You would need to cut the town down to be the same size as the original so that it can have clearance under the sash. Would that be possible?

Alternate image for 18-171

Alternate view of 18-171

Sounds good! Please let me know if we can be of any further assistance.