Is it a US thesis? You might just have to order a printed copy. I purchased a copy of a US thesis on my topic through ProQuest. Annoying that my Uni doesn't subscribe to their electronic copies but it wasn't more expensive than books in my field and it was directly related to my topic. I had to wait about three or four weeks for it to arrive though, as I recall.
Otherwise try to speaking to staff at the big copyright libraries (British Library, Bodleian Oxford, UL in Cambridge) - they might be able to help and if you are an HE student at another British uni you can get a ticket to use some of their facilities.