Mackerel Sky is available in Kindle and ePub formats, as well as print-on-demand.
books2read.com/OwensMackerelSky – where you can find the ePub versions via various providers.
Book Depository – for print-on-demand (with free shipping!)
Amazon for Kindle and print-on-demand
Threatening Sky is available in Kindle. It will shortly also be available in print-on-demand and ePub formats.