Library Hub Discover will find you books in other libraries in the UK (plus Dublin).
Library Hub Discover does not tell you which of the libraries it lists you can access. For this info see:
Important libraries in London for the study of art business include:
One of the three largest libraries in the world. Offers many business databases, though only for consultation from the British Library's own computers. The librarians have much expertise in business research and offer an online guide to business and management studies. Register for the Management & Business Studies Portal to download various business reports and papers to your own device, from any location. Registration is very quick and easy once you have set up a BL online account.
National Art Library
At the V&A. Very useful for obscure sales catalogues, books about patronage, and much else.
Westminster Business Library
Public library. Gives access to business databases not available at SIA. Not included in Library Hub Discover.
Wiener Holocaust Library
Small specialist library, worth investigating if you have particular interest in the effect of the Holocaust (or other genocides) on art.
WorldCat will find you books in other libraries worldwide. Coverage is uneven; e.g. there are some major African cities with no libraries included.
The SIA librarians will help you find books and access libraries anywhere in the world: though please note our knowledge of many countries is limited.