Opps, I just saw you want one to buy, disregard. But if you can't find anything, this is really easy and works great!
I use actual corks (real cork or rubber) from a local hardware store. A good store will have various sizes ranging from 1 inch down to 1/8 inch. Mine are 1/8 inch, and too small to fashion a lanyard, but are painted yellow (or red if like) and I count them before I go. Keep nicely in pill bottle.
If you went that route, a 5/8 inch cork would be big enough to drill a hole down the middle, and use shoe lace (or 550 cord if you are military) through it, with a knot and glue to lanyard up. The lace threaded through the smaller end with knot keeping it from going all the way through; glue for extra security.
Probably other ways, but an idea to consider. My problem is spiders building mud nests in fuel drains and vents; frustrating!