Not sure what you're looking for: Items that had been cross-referenced, but aren't any more (why would you need to "rebuild them"?), or cross references to items that no longer exist (how would your macro manage to rebuild them?).
If the latter:
The cross references show an error message, right?
.... something like "Error! Reference source not found."
You can use "Edit > Find" to search for that error message, to at least locate them.