There is no offical locking device for the Blink cameras.
Other users have come up with some pretty creative housing to help.
I can say that I’ve never had an issue with anyone messing with my cameras, though I’m sure there are people out there that would. My black cameras are also mounted in shaded areas, against dark brick. You’d have to look really hard to spot them.
I’m also not sure any of the competition has locking devices either.