Up until last week, the only way to buy a PDF and a print version of Sock Architecture at the same time (and for a good price) was by going to http://cooperativepress.com/ to do it.
Well, they're clearing out their warehouse and my book has sold out, for now, from them. A little note on my book's page on their site now says this:
"As mentioned in our most recent email to the CP mailing list, we are currently transitioning to a new sales method for our books. Our new website will go live shortly, and in the meantime, we are working to clear our warehouse of excess inventory. Some book titles have oversold, and this is one of them. We are shipping books to fill those orders now. In the meantime, if you would like to order a copy of this book, you can find it on Amazon here. If you purchase on Amazon now, you can forward a copy of your receipt to us at email@example.com with your Ravelry username and we'll put it in your library there."
So, if you've been waiting to buy it, this might be a good time to, since I don't know how long they will offer a bundle deal!