Great question — answering as the UphillTech team:
Visit your favourite sewing store and ask for a "separating pin set" for a zipper. You'll need to know the size and the type (e.g. brass teeth or nylon coil).
Full answer by Ray Butterworth: https://lifehacks.stackexchange.com/a/27056 (CC BY-SA 4.0).
Need it done for your business? UphillTech.