When we replaced our slider with one from the local home center, the metal rail was held into place in the door jamb with two or three screws up into the top of the jamb. Can you see if that is how yours is put in place?
I did consider using the existing sliders, since they were still in place, but I can't recall now how they attached to the door itself. If you can find a way to attach them to the new door, that might work. But surely the metal rail had a method of attachment...
Let me know what you find, if need be I can take a look at ours and maybe send you a pic or something.
"Airabelle" - '66 Overlander International 26'
"Mod-Pod" - '77 Argosy Minuet 6.0