I would have thought that the 555 timer would be in its element at these sorts of frequencies?
I agree with RonH ...
I don't understand why you want a 50/50 mark-space ratio, I think this is just adding to the difficulty of the design. Either make it as narrow a pulse as possible (audibly just a 'click') and have one pulse per music beat, either that or use a series capacitor followed by a diode to ground so that only positive-going edges come through to be heard at the output?
RonH The gated tone is just a nice way of making the audible 'click', imagine a drummer tapping a nice steady beat- I think a narrow pulse to a speaker cone could sound similar ?.
Optikon Whilst the divider idea would give brilliant stability I would think it needs to be adjusted in steps much smaller than 1/4 second (equivalent to 15 beats per minute) to be truly useful in music - your idea could be adapted to 1/60 second increments to allow setting to the nearest integer beat per minute ?