This wouldn't be on Dainese gear, by any chance...?
Whenever it happens to me, I try to find a small key ring and feed it through the bit on the top of the zip closer that the pull was originally fitted to and then, if necessary put something through the key ring to grab onto.
Once upon a time, Graham Tiso used to sell black plastic zip pull extensions but they don't seem to stock them anymore.....
In the past I've used very small, thin zip ties - not the perfect solution but pretty good. But I've got Rukka stuff now so won't need that solution anymore
Sewing department in Peter Jones (they call it Haberdashery, whatever that entails) sell replacement pulls, but some of them don't have the real biker look. Cute shop assistants though!