These brushes were originally created for PS by 77words, who most graciously allowed to convert them into .gbr format, so that they can be used in GIMP. Please credit her and not this account which only serves as a collection of resources. 77words originally posted the brushes here. You can give her feedback there.
77words' original PS brushes, icons and other resources 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.
For 1024x640, hit fullview and grab it from there.
Rare treat, something for the widesceeners out there, hopefully the resolutions & such are right and the whole thing won´t look too crappy. Will be also included in the sixth cosmospack for *resurgere when the time for it comes, if I´m still feeling generous enough at that point.