You can work backwards to find all of the Users that have a Bridge Appearance for some other User, then look at the Button Programming for each of these users to see whose Bridged Appearances they have.
Export the entire configuration as csv
Trim it to the section User Info Start to User Info End
Search for "SetBridgeAppearance", which will take you to Column AE (US_ShortCodes) and the Row of a User that has a Bridged appearance for someone else. Move back over to Column A or D of the same Row to get the Name of the User, or Column E to get the Extension Number of the User.