Kudo's to Tor for this excellent tip. After a trip to Hornby Island in January where the Stellar Sealions chomped and mangled at least three of my fibre optic cables, I was looking a couple hundred dollars to by all need cables and spares. I started looking into various DIY suggestions, including the use of old Toslink cables. I found the Toslink worked ok, but the fibres were really very thin. I've had reliability problems even with purpose-built cables transmitting enough light.
I decided to try out this suggestion and purchased 5 meters of the 3mm end glow optical fiber recommend here from Amazon at a cost of about $15 US. I already had some modular end plugs form existing (mangled) cables to reuse. It works great! The 3mm cable is very sturdy and transmits a lot of light for a strong signal. I used velcro strip to attach it to my arms, and a bit of Sugru on the end caps to prevent too much bending at the attachment point. Bonus - I have about 2.5 meters of cable in reserve for replacement spares in the field.