Plenty of people looking but few are succesful unfortunately. As far as I'm aware, all of the Waggot heads are accounted for at the moment. That is, they're in the hands of known collectors/museums, so it's unlikely that you'll happen to stumble across one.
About 12 months ago I knew of a Waggot head that was potentially for sale. The owner had a figure in his mind around the $70,000 mark though.
If you're dead set on having a twin cam head. Have a chat to a respected machinist/engine builder and you might be able to discuss having one made. Either from scratch or using components from an existing twin cam motor.
A reproduction crossflow head might be the simpler way to go. And much more affordable too