A couple of days ago, Tales from High Towers' Study began selling like moderately warm cakes over on Amazon.com. I'm in the UK so I couldn't figure out why, but it seems they've finally noticed it's available free at some of their competitors' sites. So it's available free there too. That's how I intended it to be, so enjoy!
If you just must grab your e-books from Amazon and want to try out the Thaumatology universe, you can find it here: https://www.amazon.com/dp/B006ZAJ7TY