I've had this on my trek cyclocross since 2016. Says currently unavailable, so don't know if you're out of luck. Could check their website or maybe contact them. Was $45 in 2016 when I bought it. Used it with the hero 4 until I recently upgraded to the hero 9.

https://www.amazon.com/gp/product/B005YVTKT2/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1