Where Can I Find This Rubber Cord?

I recently purchased a necklace on Etsy.


I love it,especially the comfortable and free black rubber cord it came with.

I contacted the seller to ask questions, but she did not answer me back.

I'd love to find this kind of cord with its fantastic detachable clasp.

I've attached the photo.

Basically, the entire cord is rubber, with a sort of breakaway safety clasp.

I've been looking on-line for a while to see where I can find it, but the only rubber cord I see to purchase is either on the spool, or comes with a sterling clasp.

I'm wondering if maybe this is a patented design that I shouldn't be looking into, but I thought it was worth asking.

I've also wondered if maybe it is not really a jewelry item, but instead a hardware or medical item being used as jewelry cord.

Any ideas?