The ACLU's Arizona affiliate, ACLU-AZ, now supports the right to bear arms. From its Tough Questions about ACLU Positions policy FAQ:
The ACLU of Arizona, which is based in Phoenix, supports the individual right to bear arms – a right that is expressly identified in Article 2, Section 26 of the Arizona Constitution. In 2008, the U.S. Supreme Court in D.C. v. Heller held for the first time that the Second Amendment protects an individual's right to keep and bear arms, whether or not associated with a state militia. In July 2008, the ACLU of Arizona Board of Directors passed the following policy: “Resolved that ACLU of Arizona does not follow national board policy #47 that the right to bear arms is a collective, not an individual right. The Arizona Constitution expressly provides that the right to bear arms, to the extent constitutionally protected, is an individual right, so policy #47 has never been operative in Arizona.”
"Never been operative" is a bit Orwellian; the Board of Directors during my tenure as a member acted as though the National policy was operative. Former Executive Director Eleanor Eisenberg's explicitly anti-RKBA and downright hoplophobic legislative testimonies against liberalization were nonetheless never official ACLU-AZ position. She was advised by the Board to cease opposing RKBA, followed this instruction for a while, and then became rather insubordinate about the matter around the time she resigned, but events played out in such a way that there was never time for a reprimand. No doubt Eleanor turned off the marginal gun owner to the ACLU; the organization's new affirmative pro-RKBA stance could bring such people back, were it actually publicized.