Right, so: the DA. Because as incredible as this is: neither ICANN nor ISOC are controlled or run by the federal government.
As much as people think that the organization that oversees internet naming must be federal (because how could it not be, they control stuff for the ENTIRE COUNTRY AND BEYOND), both ICANN and ISOC are literally just private industry non-profit organisations, like any other 501c3. If you want to sue them, or you want them sued by government, you're going to have to contact the DA for the state(s) they are registered in.