damaged sliding patio door track

I am trying to locate something called a cap for the middle metal slider on the bottom of the patio track. Mine is damaged by the door and it is now all wavey. I saw an article stating that instead of having to replace the door or the track, someone has these things that fits right over the damaged track to make it like new. My local home improvement center doesn't carry them and didn't know where to get them. If anyone has heard of this and knows where to get them PLEASE HELP! My door is getting worse everyday. (by the way, it is not the rollers and the door doesn't need adjusting) Any input would be appreciated.