Triple track storm window repair.
I'm not sure exactly what you need, unfortunately. If you don't have any of the original hardware used to construct the screen then I am not sure what to recommend. All of our parts are made to replace very specific hardware, especially for screen and storm panels. Do you have an identical screen in the house that still uses its original hardware?
You can also browse through our selection here. If you have no originals to go by then the best we can do is guess, and our guesses will be based entirely on dimensions. You can look through here to see if you can find something that will work or, at the very least, to get a good idea of what kind of dimensions we need to make our guess a little easier.
The orginal hardware must have been the vinyl which is breaking. These are Seasonall brand triple track windows from the Philadelphia area. I'm looking at your Seasonall slide bolt set. They are written up for storm windows but would they be also for the screens? The corner keys and tilt keys I'm still not sure about. Attached are two photos of my screen frames. The internal track where the keys are in measure 3/8" x 3/16". Any easy way to get the broken pieces out?
My recommendation is to contact a local glass shop that still makes replacement screens or storms. Storm windows are a dying breed and in all likelihood you will need to have new frames custom made from scratch to the specifications of your window.