I would reccomennd this chap, i've used him a couple of times, a little bit pricey, but you get what your after, and even after he's found the book, before its sent, he contacts you, and you have the option of not having it, at no cost.
Before you employ the services a booksearcher, it's always best to check out the same places that they do. I'd be prepared to bet that the first place most booksearchers check is the UK's biggest secondhand book website, Abebooks. If they find a copy they'll then offer it to you with a hefty mark-up added on.