I don't know of one either, but if there is such a thing I'd like to hear about it.
As far as I am concerned, you just have to cut the curve into the mask. I use plain inkjet paper and Dotto for a lot of my masks, and I save them for as long as they are usable. I have a folder full of inky inkjet paper masks.
I should probably break down and get some actual masking film. Then they would last longer. I wish the Eclipse masking tape would be available in those wide rolls again. I don't see it anywhere online.