I have said elsewhere on this site (in the Dobrý den thread) that it is used in Australia and I am well aware of it. It is usually contracted to G'd day though.
It was also used regularly in the Microsoft Flight Simulator for the AI ATC. I am also fully aware of that and have always been.
I see we do now accept Good day and A good day as a correct answer for Dobrý den as it is a course of Czech. But if you take the reverse teaching English tree it will very likely still not be accepted and should not be, in my opinion. I do not remember hearing Good day at all when I was living in the UK.