Amazon.com: Princeton Aqua Elite, Series 4850, Synthetic Kolinsky Watercolor Paint Brush,Quill, 6
Da Vinci Kagalovska Watercolor Brush Quill - Various Sizes – Greenleaf & Blueberry
Jackson's Icon Quill brushes - Jackson's Art Blog
Trekell Watercolor Brush Set - Professional Brushes for Artists – Trekell Art Supplies
Amazon.com: OOKU Professional Quill Brushes Watercolor Set - 10 Pc Real Squirrel Hair Blend Brushes for Consistent Flow - Short Handle Round Paint Brush for Artists, Painting, and Gouache
Amazon.com: OOKU Professional Quill Brushes Watercolor Set - 6 Pc Real Squirrel Hair Blend Brushes for Consistent Flow - Short Handle Round Paint Brush for Artists, Painting, and Gouache