So The Silver Mask ebook is now available to buy/pre-order at iBooks and Amazon.
The paperback is available to buy at Amazon (and, based on the proof copy, looks very nice in my, admittedly biased, opinion).
I had originally planned to make it available for pre-order from today with it being available to buy from 5 August. However, some things went screwy with the settings (likely user error) and it’s available to buy now (the ebook on Amazon is still showing as pre-order, I’m trying to sort out the settings to release is as soon as possible).
EDIT: Just to note that it seems that the easiest way to find it on either store is to search for ‘The Vasini Chronicles’.