Can astronomical radio sources be used as a verifiable randomness beacon?
I see two problems.  1) Any particular source in the sky is above the horizon for a limited region of the Earth at a given time, so one would need to relay the signal around the globe.  2) It is hard to think of an astronomical source that is truly random all of the time.  Astronomical sources are physical systems reacting to internal and environmental changes that are causal, so they all tend to be partially quasiperiodic to some degree or become temporarily nearly periodic.  So it depends on just how random you need them to be, but I doubt any astronomical source is dependable for this purpose.