The Dark Lord's Handbook is available as a Kindle eBook (UK store, US Store) .
There are free Kindle readers for most platforms (PC/Mac/phone/tablet) so you don't need a Kindle device to read the book.
The book is available for iBooks through the iTunes store.
A paperback copy is available from Lulu.
For other eBook readers you can buy the ePub, PDF, RTF and LRF formats from Smashwords.