Collectors' rhymes with:
collector's, collectors, collector's, collectors, collector's, collectors, electors, lechters, reflectors, collector's, collectors, connectors, defectors, detectors, director's, directors, directors', electors, hector's, injectors, inspector's, inspectors, inspectors', lechters, objectors, projectors, protectors, reflectors, sector's, sectors, specter's, spektr's, vectors
Collectors' sounds like:
cloisters, clusters, collector's, collectors