Textures can be taken from anything.
Anything that resemble something dirty can be everything, I\'m serious.
Usually on my drawings there are only two or three textures changed to look like they are another 10.
Right now I take my pics with my cam. There are six things that, if you have pics of them, you can do virtually anything:
Metal Bars
Wood Tables
Tree Woods
Dirty grounds
Walls
Grass
For non-commercial purposes, you can use the google images search function.
Or you can paint them from the zero, in photoshop... thats a good way to improve your 2d skills which you will eventually need to fine-touch your pics.