Have you looked at getting what you want from Mill Hill – the UK agents for Sherline. I have a 1042 (ER Thread) chuck on order from them. Cost from them was about the same as buying direct from the US once the shipping, 5% duty, 20% VAT and the couriers processing fees (£12-18) were added in.
If its a stock item with them, they will also be quicker. My Chuck is not something they carry, but were perfectly happy to order me one for shipment in their next order.