Contractors' rhymes with:
detractors, tractors, detractors, refractors, tractors, actor's, actors, actors', detractors, factors, factors', reactor's, reactors, refractors, tractors
detractors, tractors, detractors, refractors, tractors, actor's, actors, actors', detractors, factors, factors', reactor's, reactors, refractors, tractors