This question was a little over my head, so I consulted an expert, Wayne Price. The following is his response, lightly edited and with some links added by your Radical Reference volunteer.

Kropotkin discussed morality in his Mutual Aid and in his unfinished book Ethics. Mutual Aid, at least, is widely available. Brian Morris (2004) Kropotkin: The Politics of Community, Humanity Books, has a chapter on Ethical Naturalism as well one on Mutual Aid. Murray Bookchin has written several works relating his social ecology/anarchism to philosophical issues, including ethics. His views are summarized in Bookchin (1996) The Philosophy of Social Ecology, Montreal/NY: Black Rose Press. This includes two chapters on Ecological Ethics.

Other than that, most anarchists who deal with ethics usually relate their thinking to some broader school of ethics. For example, Todd May (1994) The Political Philosophy of Poststructuralist Anarchism, Penn. State Univ. Press, relates anarchism to Foucault et al, including a discussion of ethics. Martin Buber Paths in Utopia is not explicit, but is associated with his own writing on ethics and human relationships (I and Thou). The anarchist-pacifist Paul Goodman rarely discussed it but he was deeply committed to Deweyan pragmatism/instrumentalism in relation to ethics and truth. (This is central, also, to my thinking on this topic.)

From the last sentence, it sounds like your questioner would be interested in the psychological literature on anger management in psychotherapy/counseling. It makes a strong distinction between appropriate assertiveness and hostile aggression. Anyway, to go back to Buber, he might cite Rabbi Hillel, "If I am not for myself, who will be? But if I am only for myself, what am I? And if not now, when?" (I know that's a weird site to link to, but it's the first one that gave a citation for the quote.)