Here are 3 refernces/articles about the evolution of Gandhian philosophy on Ahimsa( Non violence) and Satyagraha (passive resistance):

1. About how Gandhi’s ideas shaped, particularly in S Africa. Click

2. The book by Tolstoy which influenced Gandhi most and he had actually read it in 1994.
Click

3. Comparison between Adinballou, Tolstoy and Gandhi. Click

Here are more links to the themes of non-violenece, peace and satyagraha:

1. Albert Einstein Institution (based in East Boston, MA): Click on this link
Here you can find 198 methods of non-violent actions which were originally complied by Gene
Sharp.
2. Gene Sharp: Click here to read about him.

3. Mahatma Gandhi Library: Texas based. Click here. You can find the list of books by and on Gandhi.

4. Bethesda, MD based Gandhi Memorial Center: Click

5. Raj Mohan Gandhi (son of DevDas Gandhi, 4th son of Gandhiji): Click

6. Arun Manilal Gandhi: He is grand-son of Gandhiji and lives in USA and heads the MK Gandhi Institute for Non-violence (link) . His son is Tushar Gandhi. He lives in Mumbai and unlike his great grandfather, as per media he eats meat. He contested LS elections as a Samajwadi- Congress party in 1997.