Serious answer - There really isn't any large-scale alt-left movement in the US. Antifa is growing, so that would be the closest one at this point, but still doesn't have that many members.
Part of the problem is one of perception. The US has become so highly right leaning that most people don't recognize the center anymore. Bernie Sanders, while left-leaning, was actually far closer to center than any of the Republican or Democratic candidates.
Let's put it in terms of math.
An alt-left person would say: 2+2 = 1
An alt-right person would say: 2+2 = 7
The center is actually: 2+2 = 4
But people's perceptions are so messed up because we live in a "2+2 = 5" to "2+2 = 7" environment that "2+2 = 4" seems horribly left-leaning. From the vantage of the "2+2 = 6" person, all those "2+2 = 5" and "2+2 = 4" people are left of them, so a "2+2 = 3" person
feels like they are alt-left, when they are only mildly left.