If you didn’t know, all GIMP versions greater than v2.4 can load Photoshop brushes. To do it, you need to figure out where the GIMP stores your brushes and just copy the .ABR files to that location. You can find out where by clicking Edit > Preferences. Expand the Folders list and select Brushes. There should be a path with the writable option selected. That is where you should save your brushes.
I will probably create a new page for this blog with resources like this that I use frequently. Once it’s created, I’ll post about it.