The method I used was include in the end pages of all my books, a thumbnail of all the books ( I knew I was going to make!) in a series and state they will become available in XX months and to check www.xxxxxxx.com for further information.
You can also ask if the want to be notified by email, most wont due to ever present spammers.
As they became available I used Apples link maker to add logo to the web pages.
An option for you is to add the information in the original book and re-deliver as a new version, those who have that book will be able to update and see your new info.
If you check into your iTunes Connect > Deliver your Content > Featured Resourses - you will find a number of PDFs to download, one of which is iStore Marketting. It may give you some pointers.