Socialists' rhymes with:
specialists', analyst's, analysts', catalyst's, centralists, colonialists, criminalist's, criminalists, cyclists, editorialists, environmentalists, environmentalists', evangelists, fatalists, federalists, fundamentalists, generalists, imperialists, individualists, industrialists, instrumentalists, internationalists, journalist's, journalists', loyalists, medalist's, medalists, moralists, motorcyclists, nationalists, naturalists, panelists, populists, semifinalists, specialists', spiritualists, survivalists
Socialists' sounds like:
scholastic, selects, silajdzic, silajdzic's, silicates, skylights, slights, socialistic, socialists, sociologists, solicitous, solicits, soloists, solstice, solstices, squillacote's