I'm also certain there's stock available to short. The last time I checked there were about 300k short, down from approx. 850k in March 99. I know the person that covered the 500k in March. He was using it as a hedge against another investment in the sector. He covered the short after the company failed to include certain revenue in 4Q results, which were reported in March.
What your broker should have told you is his didn't have stock available to short. WHC is not widely held and not all firms have stock. However, if you pushed the issue, I'm certain your broker's firm could borrow stock from another that holds stock.