Storm window hardware

Hello,

I have a bunch of storm window/screens where the top corner piece of plastic has broken to it won't stay in the track properly. The previous owner of the house just taped them and called it a day but I would like to fix them properly. I included a picture of the top piece that is broken (of one that is not broken) and the bottom corner with measurements. I also need slide latches but I think 91-001P would work. Any help you could give me on finding the right part I would greatly appreciate it. Thank,
Martin