In case you are unable to find the book or article you require in FLEX and you don't have your own scan or digital copy to upload you have the option to order a copy from the British Library or you can use this form to request a work to be provided by a publisher.
Click on the 'Publisher Request Form' and provide as much detail as you can.
Please note there is no guarantee that the work is available in digital format and the publisher may choose to not provide it for FLEX. In some cases, it can take a few weeks or months before the title becomes available in FLEX.