Make your own like this. Lathe a slug of one inch cold roll steel to the diameter of the inside of the bar leaving a bit at full diameter outside.
I did mine so that it also served as a bar extension and bar end weight also. Rebait the outer end to recess the head of an allen bolt.
Balony slice it so that when it is inserted into the end of the handlebar, the allen bolt can be tightened to cause the diagonal to lock it to the inside of the bar. (Yes it works on the throttle side too.
Machine a piece of alumnium to be the end cap and drill through the end cap when it is in place to fit it for a roll pin the keeps it from ever coming off accidentally.
To deliberately remove it, just use a pin punch smaller than the roll pin to drift the pin into the rebait void and remove the cap. Then unscrew the allen part way and tap on the end of the allen to unlock the ar end device.
Easy huh?
Phelonius BTW the small pocket knife and the lighter are in the photo for size comparison.