http://www.deviantart.com - search for brusher's there, mainly grunge, abstract, tech, stuff like that.
Then when you load photoshop, make sure you have the brush tool selected, then in the left hand corner there should be a little circle, click that and one of the options should be add brusher's, click that, go to where you saved them and double click the brush you want to load, and it will load into your default brusher's.
(Ive not used PS for over 2 months so if that dosnt work out for you ill open up PS and take some screen shots to explane it a little better.