Here is a scan of two "Province of Bumbunga" stamps:
The first, denomination 35 cents, features an image of Prince Charles windsurfing, and is inscribed "SURFING, WESTERN AUSTRALIA".
The second, denomination 50 cents, features an image of Prince Charles on a horse, and is inscribed "POLO, WINDSOR, U.K."
Stampboards "A to Z" Compendium of Philatelic Terms -http://www.stampboards.com/viewtopic.php?t=7580
has this relevant entry:
Bumbunga Province: bogus Australian secessionist state three hectares north of Adelaide.
How much are these two cinderella stamps worth?