sugarplumkitten creates 'em, and I convert and post 'em. Please credit her, as I only converted them to a format usable in GIMP.
Original PS brushes can be found here
at her Livejournal.
To install, unzip files into the brushes folder in your GIMP program files (usually C:\Program Files\GIMP-2.0\share\gimp\2.0\brushes in Windows or /home/username/GIMP-2.0/share/gimp/2.0/brushes in Linux) and then restart GIMP.