Registrars rhymes with:
aerostar's, aerostars, avatars, boxcars, cojimar's, escobar's, feldspars, gaidar's, handlebars, hectares, jaguar's, jaguars, magyars, melkar's, memoirs, minstar's, mizar's, morningstar's, motorcars, northstar's, radars, railcars, reservoirs, seminars, seskar's, sidebars, tigar's, windstar's
Registrars sounds like:
racetrack, racetracks, racketeers, reactor's, reactors, register's, registers, registries, resistors, restores, roasters, rochester's, roister's, roosters, rosters, royster's