RTL 715 rear rack mount needed

Look at gopro mounts there is a huge market of aftermarket stuff.  The 715 uses a different interface than other garmin quarter turn stuff which makes things a little trickier.  But maybe these two items?  Swap out the quarter turn part with the item in the first link? FYI, I use the saddle rail mount I've linked to across three different bikes with my varia 515, works great.

https://www.magcad-designs.com/products/magcad-garmin-varia-rct715-gopro-mount

https://www.amazon.com/Cestbon-Garmin-Rtl510-Rearview-Bicycle/dp/B0B92B9M8M/ref=asc_df_B0B92B9M8M/?tag=hyprod-20&linkCode=df0&hvadid=647237004205&hvpos=&hvnetw=g&hvrand=3817858430858770005&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021307&hvtargid=pla-1930176402382&mcid=2d953945809a30209ac128a562e665ca&th=1

EDIT: just realized you aren't looking for saddle/seapost mounting.  Nonetheless, I suggest looking into a gopro style adapter since there is a big market out there for that.

Thanks for the steer in the right direction.

You can make something using a stem cap Garmin mount plus a big P clip and a suitable nut and bolt. Here's an example I made to fit a Carradice Bagman.

Hi. I have the same issue. Got a 3D printed thing which worked well initially but wore fast and is now not fit for purpose. Found this on Amazon and although on the dot com site says it ships to UK. I can let you know if it arrives if you like. www.amazon.com/.../ref=ppx_od_dt_b_asin_title_s00