If you define a Style for your dialogues (probably a character Style), you could use a wildcard Find/Replace with:
Find = ^0145[!^0145]@[.,\?\!][^0146]
Replace = ^&
and specify your dialogue Style as the replacement Style.

Having done that, you could use an ordinary Find/Replace to look for your content in whatever other Style the rest of your document uses for the body text.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]