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.
I really think youd be fine without a pattern...I got a cheap one alot smaller with animal print(yuck) for a gift after ds was born...Ive been dying to make a new one just havent gotten around to it lol
Another thing I have done is use a single layer of flannel, like a receiving blanket but much larger (maybe 45x60 or so??) and tuck it behind my shoulder or under my bra strap on one side and sit on the other side. It is thin enough that they don't get too hot, you are fully covered, and it doubles as a blankie. Plus you can get any fabric you like and just hem the unfinished edges.
"I'm so crafty, I make people" DD (01/06) and her much anticipated sibling (07/10) with my sweet DH (07/02)