Downloadable .STL files
Have your own printer? These files are designed to be printed in flexible material. They are released under the OHWS / Creative Commons licencing agreements.
Be cool and do not sell the design, only print it for yourself. The two pieces need to be welded together with a 3D pen / soldering iron.
https://www.thingiverse.com/thing:2985825 (full brush)
https://www.thingiverse.com/thing:3071186 (mini brush)