As of October 2015, 31 states (including Washington D.C.) have passed benefit corporation legislation. Most states' final laws closely resemble the benefit corporation model legislation, though a few deviate in significant ways. For an example comparison between contrasting requirements in Delaware and California regarding accountability, transparency and incorporation, see this two-part article (here and here).
If you would like to find a benefit corporation in your area, we recommend the tool available at BenefitCorp.net. While we cannot vouch for its to-the-minute accuracy, as reporting requirements vary greatly across states, it maintains a generally useful index that can be searched by name and region.
Below is a state-by-state index of links to benefit corporation legislation and, where available, state-specific "How To Become a Benefit Corporation" guides created by B Lab.