Who can I get to fix broken cord on pull cord drapery track?

My parents have the "old fashioned" for lack of a better word, drapery track over the living room window, that sits into a valance box. The cord at the side of the window you pull to open or close the drapes.
This cord due to age, I am sure, has snapped, and the drapes cannot be opened nor closed.
Is there a company that will restring the track, or do something to fix or replace this so that the whole track does not have to be removed.
thank you