You can run a piece of 2" or 3" velcro under the magnet mount...
https://www.amazon.com/Tac-Mag-Gun-Magnet-25-Rating/dp/B00LR454YU/
$12 + the cost of the velcro.
That's cheaper than a purpose-built mount.
Pretty hard to rattle loose from that magnet, if that's potentially a problem use 2x...