The first is that they are all vinyl construction, including the frames. These are common in replacement windows manufactured in the last 25 years. If this is the case with your windows, you may be out of luck because the "tracks" in which the sashes slide are an integral part of the frame of the window. I know of no remedy other than the replacement of the main frames. If the windows are over ten years old, chances the vinyl extruded frames are no longer manufactured. Having said that, you may have a warranty claim if you were the original purchaser of the windows.
The second is if the windows are basically aluminum with a snap in vinyl track. In this case, replacement tracks are likely available. Pickens Window Service in Cincinnati, OH should be a national treasure. They are simply the best source of window parts in the USA. They stock the most hard to find parts for windows manufactured at almost anytime in US history. You can visit their website at:
http://www.pickenswindowparts.com/
Good luck with your search.