Some Magpie had away with my CT200 valve dust caps too.
I bought a set from Halfords that can only be removed with a special key. Without the key, the body of the cap just spins round.
Nice-looking chrome too.
There was another set that had the hex spanner body and locked on with a grub screw. I didn't get these because I suspect that someone could wrench them off with a spanner and trash the valve in the process.
I just hope that the Magpie is enjoying having Lexus valve dust caps on his push-bike.