I never found a pattern so I just plunged in with my dresden ruler and made one following a picture from Pinterest. I figured out that for a 12" block, you need "blades" that are 5" long (5), 4" long (10), and 3" (5). Altogether, 20 blades.
Here's mine:
It's for one of the ladies in the Boom block swap. She's doing a Christmas quilt.