There are lots of repositories for theses. Just put thesis repository into Google, you’ll find plenty of options. If I do it, the first options are in Australia. Your local library will probably have access to databases you have to pay for too.
The British Library has a service. From the site:
What theses does EThOS have?
EThOS aims to hold a record for all doctoral theses awarded by all UK universities (institutions). There are some gaps which we are gradually filling, but there is a record for at least 90% of all UK theses, some 400,000 records.
EThOS also provides free, direct access to the full text of as many theses as possible.