Not really anywhere free. I do have a couple of suggestions though.

1) Every time you're on a shoot, make it a point to shoot a few angles and minutes of whatever is around you and unique. I have a library of moon, sunrise, sunset, traffic, aircraft, bugs, flowers, trees, people interacting on the street, malls, etc. Just shoot! As a rule, I do this at the start when I'm setting up for a shoot (white balance, testing the camera, light etc) and before I shut down. I also carry my "stock tape" so it's all in the same place.

2) http://www.istockphoto.com is one of the better and cheaper sites out there. Plus, if you subscribe, you can get a free image and clip per week. The price is right, and it just adds to the library.

Just a thought.

ps: I also have set aside a few days for the types of shots that I think I'll need and then just spend a day relaxing and shooting stock. It's not nearly as tedious as you'd think. And in the end, can be a heck of a lot cheaper. Once I found a street sign that said "Street Avenue"