1.)Download brushes you like even if theyre for PhotoShop
2.)Open downloaded file copy the brushes/rick click>copy
3.)Do this STARTBUTTON>COMPUTER>OPEN C:>PROGRAMFILES(x86)>FIND GIMP-2.0>SHARE>GIMP>2.0>BRUSHES>PASTE DOWNLOADED BRUSHES FOR PHOTOSHOP/GIMP IN BRUSHES
idk if this was posted already but if its not this is what i did :).
----proof-----
https://img849.imageshack.us/img849/5582/proofw.jpg