I remember seeing it in the wild three times. The first time was when I got my copy at an EB in 2005. It was a brand new copy they had to mark as a used game for whatever reason, but everything was minty. Set me back $3.99.
Since then, I've seen a loose cart at a CD/Game Exchange at some point in 2006, and another loose copy at a GameCrazy last summer, and that's been it.