I'm using the old edition 9/30/2015 N400 forms and I need to add additional information, where can I find the old version?

The USCIS has asserted that, starting on August 8, 2016, it will accept only the March 26, 2016 edition of the Form N-400. Until then, the USCIS will continue to allow cases to be filed using the September 13, 2013 edition of the Form. Even for a case filed before August 8, 2016, it may be advantageous in the adjudication process to use the most recent form. Especially if you have concerns that there may be a complication or problem in using the new form, it would be wise for you to consult with an immigration attorney who, after learning all of the relevant details about your situation, could advise about eligibility and could offer legal representation in the process of applying to become a naturalized citizen - a process that often can be far more complex than it appears merely from reviewing the form and its instructions.