I know this is going to sound terrible but I had also wondered about getting this ruler... I clicked on enlarge on the computer then held up my half circle rulers and wouldn't you know it... it's just a section of that ruler... nothing special about the shape. It's a 10 or 10 1/2" section of a 10" circle. So if you use a 10" circle ruler, you can mark off 10 or 10 1/2" of that ruler. The overflow on the ruler she has is just for the size of the rotary cutter. I'm only saying 10 or 10 1/2" because if the block is 10 1/2" when finished then that's the size that you'd need. I suspect it's 10 1/2" but I haven't looked at the pattern yet to confirm that. You can give it a try and see how it goes...
Her Urban Nine Patch pattern that's free online had looked familiar to me... it's in one of my really old classic quilt blocks books. I have been meaning to do a quilt using that block but haven't gotten around to it yet... one of these days...
Where is the quilt a long going on? Maybe it will inspire me to actually try out my theory
I found these two online... I might have to join in on them. I love curves
http://thecreamsiclecat.wordpress.co...r-quilt-along/
http://sewkindofwonderful.blogspot.com/