My suggestion is to let someone like Diggory Hadoke of Vintage Guns UK or John Farugia of Cheshire Gun Room handle the deal for you. They can walk you through the paperwork and they can also eyeball the gun for you prior to shipment so you don't get stuck with a "white elephant" If you buy from one of the well known auction houses: Holt's, Bonham's, Gavin Gardiner's, etc., it is still a good idea to have a knowledgeable expert on that side of the pond look at the gun for you, but certainly do so if you buy from one of the lesser known auctions, shops or individual. JMHO
Best Regards, George