A google search for the type of brushes you are after (i.e. enter 'photoshop grunge brushes' as your search string) will usually turn up some good sites.
when searching google/msn/yahoo you can find. . .
i tried to look up some for you, but all i got was forum posts, including this one
my friend is a graphicer - i will ask him and update this post. . .
Peace
