You probably already have, but check ebay. Sometimes UK sellers have HO scale items for sale. We've always had good luck with Internet Model Trains http://www.internettrains.com
although we've never had them ship overseas. Their shipping policies seem reasonable for such.
I found these guys: http://www.ontracks.co.uk/index.php?pag ... gue&cat=84
but I don't know anything about them.
Hope that helps a little!