I have been teasing these for quite some time, and you have been asking! I finally have these quill watercolor brushes available for sale!
 
A few things to note:
The sizing on quill brushes works differently than on normal round brushes. For example as size 3 quill brush will be similar to a size 12 round brush. The size 6 quill brush could eat my normal round brush as a snack.
Quill brushes hold a TON  of water. The bristles are also arranged in a way that makes them a little less predictable, but oh do they have such a wonderful point.
The size selection might look kind of funny to you because it's 1, 3, 4, and 6. I decided on these sizes after extensive testing. I found that these were the sizes I reached for the most and had the most difference between. I didn't get bigger than a 6 because it was just too big for most things I do, and the inbetween sizes didn't have enough difference, so I figured this would be a way to help you save some money since these brushes are more pricey!
 
Details about this set:
Includes 4 quill brushes (size 1, 3, 4, and 6)
Synthetic bristles
Fun dark teal handle