Hexbear.net is anti-sectarian, so it has AnComms and Marxist-Leninists alike, with no infighting allowed. It probably has the largest number by quantity.

dbzer0 has many AnComms, though it’s explicitly a Piracy instance.

Lemmy.ml has Anarchist communities as well as the Solarpunk instance, but neither have the numbers of the other 2 instances listed.