Oh, sorry I thought was a coiled cable. Looks like it was just the rubber bands to attach to stem and bars.
I'd call Garmin directly or email them thru their website. They have pretty good customer service, maybe they'll just send you one. At the very least it shouldn't be terribly expensive.

Edit to add... this is the same USB cable to update and charge your Garmin automobile GPS, I think the only difference is the length. Maybe you could source one from eBay or from a GPS store.