To find patrons who are BARD only for DB you'll need to query on the patron Medium and Serve Code. If your library doesn't use "OB / BARD Only" then replace the OB with what you use.Quick Search
Main Status - Begins - A [if you only want active patrons]
Pat Medium - Begins - DB
Advanced Search
Media - Serve Code - Begins - OB

If you want to find patrons who are BARD Only for braille and audio, leave out the Pat Medium parameter.