I've been buying books from Amazon since they started in this country. Service has always been fast, ie next day, most of the time. Prices are normally cheaper, but don't forget to take into account the postage.
Good selection of motorsport books.
The other place to try is Sportspages. If you have not come across them, they are a specialist sports bookshop in London.
Find them at
www.sportspages.co.uk.
Good selection of motorsport books, but the prices are not normally as low as Amazon.