Capital IQ allows you to screen for companies with takeover defenses such as poison pills, anti-greenmail provision, blank check preferred stock, corporate sponsored dead hand provision, dual class stock, etc.  Screening applies to current state only.

1. Mouse over Screening and click Companies.
2. Under Takeover Defenses, click Takeover Defenses.
3. Add desired criteria to search.

GMI Ratings, available via WRDS, also allows one to screen on various types of takeover defenses.  This can be associated with a given year back to 2005.

FactSet

1. Click Screening and then Universal Screening.
2. Choose Activism/Governance and then Starter Screen - Corporate Governance.
3. Multiple screening criteria are available (for current state only), or one can get a governance profile of a particular company.