Heller's Decision is having a staggered release around the world at midnight 12 August (as 12 Aug turns into 13 Aug).
At Smashwords, it should be available at midnight North American East Coast Time. If you can't find the book in your favourite retailer, check if it's available at Smashwords.
At the Apple iBookstore, it should be released as it hits midnight in each jurisdiction (currently now available at the NZ, Aussie and UK stores).
At Kobo, it should be available at midnight North American East Coast Time.
At Amazon, look for it from 13 August (not quite sure when it will be there).
At Barnes & Noble, look for it from 13 August (not quite sure when it will be there).
At all other retailers, keep an eye out for it from 13 August. Release dates might vary from retailer to retailer.
To people on my mailing list, I only managed to contact half of you before gmail wouldn't let me send any more large emails. My apologies.
UPDATE 1: (13 Aug) Heller's Decision is now available at Smashwords, the iBookstores, Amazon and Kobo. Still waiting on Barnes & Noble.
UPDATE 2: (14 Aug) Have now been able to contact everyone on my mailing list. Apologies for the delay as I waited out the 24 hour gmail ban for mailing too many people in one day!!!
UPDATE 3: (15 Aug) Heller's Decision now at Barnes & Noble.