search for offline files

I've been using the demo version for a month now and I'm getting used to it. I've been going to and from view nx & capture nx2, comparing image quality. The noise reduction is far far superior in co7!!
With all the manipulations though, I erased a number of files with view nx, which have gone "offline" in co7. I'd like to use a filter to select them and remove them from the catalog (like you can in lightroom).
How can I do this please ?