Finding the specific texture you want online (for free, legally) can be difficult, but there are a number of ways to quickly create custom textures of medium to high quality using what you can find. Just a few general notes (Not necessarily for you):
For me, the quickest method is to use MaPZone, which is free. The biggest problem with that is you have to learn how to use MaPZone to make anything with it. The quality of results depends on your skill.
The other solution is to find multiple base textures online and then merge these into the specific image you want. In another blatant endorsement, I really enjoy ImageSynth, but that actually costs money. Similar results can be produced with any image editor, a little skill, and time.
Most online free textures only provide the diffuse image, so I recommend using a tool like Crazy Bump to analyze that image to produce the other maps. The quality is not always great, but for these purposes the generated textures should be ok. Crazy Bump is no longer free, but Nvidia has a photoshop plugin and there is one for Gimp as well.
Here are a few sites that I found in under 3 minutes (Its really not that difficult to find more):
* http://cg-india.com/free_textures.html
* http://www.tutorialsforblender3d.com/Textures/Textures_index.html (Would only use most of these as a component of another texture)
* http://www.textureking.com/
* http://www.texturise.com/?page_id=2606