You can do this if you access the Bloomberg database terminal located in Mason Hall. You'll want to type EQS <GO> into the command line interface to access the Equity Screening tool. You can specify in here that you want to 'Add Criteria' and choose 'Security Attribute' = 'Multiple Shares Available' to screen down to only those companies that issue multiple classes of stocks. Please bear in mind this database has extremely limited download capabilities.
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