There is just ONE Hiller current on the G- register, and that's a stretched E.4 model with a CofA expiry date in 1997. So, I guess the enqiry is actually prompted by the article in the May edition of Pilot mag
http://www.pilotweb.co.uk in which a UK based N reg Hiller 12C is featured. The owner of this has two others (one 12B which has been on the G register but CofA expiry was 1974!, and one 12C) all on the N register.
One of the 12Cs is featured on the owners website at
http://www.southernaircraft.co.uk - price is 40K pounds, no VAT
OK, so I am making a lot of assumptions here, but I guess the search is for an FAA examiner and not a CAA one...
The only other place I can think of in the UK that may be able to help is HFI at Gamlingay (near Old Warden and Little Gransden) - try 01767 651887 - they maintained and operated some Hillers up to a few years back.