I did some digging on this. The stock under gunnel rod holder straps use standard hardware that you can get from a kayak dealer. The top screw end and the bottom J hook end are offered and are basically compression fittings. I didn't find the rubber bungee material, but on my boat the J end broke. I simply worked the top compression fitting off and removed the J hook base. I ordered a few from this place and plan to re-use the existing rubber bungee material. You could replace the bungee with any standard 1/4" bungee material offered if desired.
I did some digging on this. The stock under gunnel rod holder straps use standard hardware that you can get from a kayak dealer. The top screw end and the bottom J hook end are offered and are basically compression fittings. I didn't find the rubber bungee material, but on my boat the J end broke. I simply worked the top compression fitting off and removed the J hook base. I ordered a few from this place and plan to re-use the existing rubber bungee material. You could replace the bungee with any standard 1/4" bungee material offered if desired.