Ebay would be your best bet! Plenty of reputable sellers with old coins there. And I don't live in the UK either! I'm Canadian, so I used a Canadian quarter, as they were the cheapest large coins with his portrait on them I could find. I found one from 1937 because that was the first year we had portraits of George VI on our coins. But an uncirculated 1951 or 1952 quarter (the last two years of his reign) look to be about half the price of an uncirculated 1937 quarter, if you wanted to go that route.