Red Iron Nights and Deadly Quicksilver Lies remain out of print, for the moment. Angry Lead Skies is definitely available as an e-book, it may be available soon as a printed book, if Amazon is correct in its listing.
The fact that you found Faded Steel Heat at Chapters now suggests that perhaps the buyers for Borders and for Barnes & Noble's brick and mortar stores decided to pass on the book, since the shelves are already full of Garrett volumes. Perhaps the reprints have stopped selling well, I see that Faded Steel Heat is #124,000 something on Amazon, while The Return of the Black Company is #7000 something.