Howard said:
The handwheels have been found on eBay before. It's just a case of checking every day, to see if someone's throwing out their old sink and taps. Usually, the auction will state 'Local pick up only' as the seller just wants to get rid of the old sink. This is how I found mine. It's then a case of convincing the seller to disconnect the taps and ship them.
However, if a plumber or builder is fitting a new sink, they'll just discard these handwheels as they're plastic, and are not recycled here in the U.K.
As has been stated, the emitter (Derwent balance pipe - or interconnect/er) is the most difficult piece to find.
If you find an engine, then you have to convince the owner / seller to take it apart to see if it has the correct type of balance pipe. I don't know the ratio, but I think it's around a 60/40 chance against finding the correct piece - from reports I've read here.
Then again, if you do find the correct engine - there's quite a few balance pipes inside!
I believe there's only 6 - 8 correct balance pipes in the hands of collectors.