You can buy one or a block of 10 or a block of 100 or whatever.
here is their how does it work page
On an ISBN application form you request either a single ISBN, generally issued to ‘one-off’ publications or a block of ISBNs. There are 2 options with a block purchase. 1. We hold the numbers at the agency and you request a number each time you have a title ready. You need to give us the title details on our application form before a number is issued. There is no charge, after your initial payment, to request a number. 2. We send through your numbers for you to keep in a safe place and allocate when needed. You do need to submit title information to us via our online service called Bowkerlink. Find out more at www.bowkerlink.com
these are the payment options and the page you will see when you want to buy.
|ISBN Options *||Quantity||Price|
|Select this option if you are requesting the next number from your managed ISBN block held at the agency.|
|When selecting a block (10 or more ISBNs) there are 2 options available, please select one: *|
|We forward all of the ISBNs in your pre-purchased block to you so that you can allocate the ISBNs as you need them. We still require that you provide title information at your earliest convenience, preferably via our online title notification system, Bowkerlink (for further details, please see BowkerLink). Bowkerlink can also provide an online logbook to help you manage your ISBNs.|
|We hold your pre-purchased block of ISBNs here at the Agency. When you have a title/titles ready for publication, you request an ISBN/ISBNs by filling in and forwarding an application form, providing title details. We will issue the ISBN/s within 5 working days. There is no charge for ISBNs issued from your pre-purchased block.|