Brian, I'm totally down with comping into live plates, either exclusively or mix-and-match with digital backgrounds. As for where to get 'em, the GOOD news is that I'm in Manhattan, which would make a pretty good stand-in. The BAD news is, I don't own a video camera
Here, my reel has a bunch of shots from my thesis project for school salted into it. The project is a few years old now and pretty rough in places, but it had a good mix of all those kinds of elements in it: valks, plates, camera tracks, digital background extension, etc.
http://homepages.nyu.edu/~pfb206/reel.mov