There are certainly overlaps between individualist anarchism and anti-civ, and there are also overlaps between what could broadly be called social anarchism and anti-civ anarchism. You are correct that these lines are not particularly easily defined, but I will see if I can try to suss out somethging more specific.Many current North American individualist anarchists also have some sort of critique of civilization (which makes sense, since civilization is completely predicated on maintaining the smooth functioning of various social relations and contracts). Individualists aren't necessarily against being social, it is more about where their priorities lay, and what sense of freedom they give primacy to. Examples of anarchists I might consider both individualists and anti-civ would include Wolfi Landstreicher, Peter Lamborn Wilson, post-leftists like Bob Black, and, so far as my reading of it, the editors of the old egoist papers Sovereign Self and My Own.There are also anti-civ anarchists who have a much more social anarchist perspective, or social anarchists with an anti-civ critique of one kind or another. Here I think of groups like crimethinc. (not necessarily explicitly social anarchists or anti-civ, but both do play roles in their overall critiques) many anarcho-primitivists (I would argue Zerzan is, at base, arguing A-P from a social anarchist perspective, even if not a left-anarchist perspective), the (now defunct) Phoenix Class War Coalition, and authors like David Watson (and some of the other Fifth Estate folks).And a lot more folks are going to be harder to pin down to specific vectors like that.
your comment on priorities is interesting; what do folks think of these definitions:
individualist anarchism: a philosophy that regards individual freedom as essential to mutual aid
social anarchism: a philosophy that regards mutual aid as essential to individual freedom.
i've long felt that this was a silly dichotomy (like most dichotomies). now i think i understand the "difference".