I don't know about sourcing an Official Fan Clue Bat but you could always try the following:

a) Visit hardware store
b) Acquire suitable length of two by four wood, adjusting as appropriate for height, arm length/strength etc.
c) Carve one end into a convenient, ergonomic handle.
d) Label with "Fan Clue Bat" in suitably large letters
e) Varnish to protect finish.

Voila! Your very own Clue By Four. :)

I of course lack the skills required for c) - d) but you're probably good to go...