Removing a vinyl window from a metal frame

Any one out "there" know of a supplier for replacing aluminum door frame parts, i.e., the bottom door track. Unfortunately, we can't locate the brand of the door, but it looks like a standard track with the rollers running on a center rail which is missing a piece just shy of the middle of the track. There is a similar, though smaller track to the interior for the Screen. This is definitely an older home, for a long-time friend of the family. At one time, to make it more energy efficient, because of the wall thickness of the bricked home, they installed an additional aluminum sliding door unit on the outside of this original. I don't think I've seen that done previously, at least personally.

I recently bought a house built in the 50s. Whoever owned it last had a kitchen and a 3rd bedroom added. The layout of the additions were probably done by a cross-eyed fruit fly or whatever pesty bug you can think of. Anyway between bedroom #2 and the kitchen they installed a nice frame for a door but no door. After taking and retaking measurements from the inside of the jambs, I have come to the conclusion that the installers were probably Larry, Moe and Shemp. The top of the jam measures 29 3/4" across and the bottom of the inside jamb measures 30 5/8" across. I am not a master craftsman. I do have experience in working with wood. But I am stumped :confused: as to how I can install a door. Lowes and HD have standard sized doors 28" and 30" doors. What can I do? Any help will give me hope! --DN