No pattern, but I don't think you'd need one. It looks to be about the size of a largish receiving blanket--in fact it looks an awful lot like a double-sided receiving blanket with a strap. And the strap is threaded through d-rings to make the neck adjustable. If you haven't done much sewing, you could check out apron patterns for that basic construction.
Now. If you plan to use a sling at all, many--most--of those can have the same function. Until dd was about 15 months, I most often used a ring sling; I'd just bring the extra fabric over to the front, if I thought I needed a little extra "cover." One less thing to mess with.
This is the sling I used--http://www.mothershavenidaho.com/Pro...ductid=2023100