I have an account on deviant. On there they have a feature called the Daily Deviation, which they award to a number of artists each day. Today’s awardees include one that links to a 4.6 gig (zipped size) library of textures, brushes, etc. According to what the poster says, this is all public domain (quoting them) -
Over the years i have gathered photos of many interesting surfaces. most of it could probably get better use from anyone who needs some nice planet like textures. so i present to you 5 gb of random photos of ice and rust and all the texture brushes i have used so far. i could keep it all to myself, but life is so busy, and i like to see what other people come up with. so have at it. use these as you like, i consider the work i have done here to be open source.
So if you are interested here is the link to the page that has the link to the stuff -
As I’m currently in the process of downloading it, I can’t comment as to the quality of the contents. Give it a try, you might find something useful.