Koop's rhymes with:
coupes, koops, recoups, scoops, coupes, drupes, dupes, group's, groups, groups', hoopes, hoops, intergroup's, koops, loops, oops, poops, recoups, scoops, soup's, soups, stoops, swoops, toops, toups, troop's, troops, troops', troupe's, troupes, whoops
Koop's sounds like:
kabuki, kafka, kafka's, kafkaesque, kaposi, kaposi's, kappes, kappus, kaps, keeps, keepsake, keepsakes, kepco, kevex, kickback, kickbacks, kiev's, kippes, kishbaugh, kobak, kobayashi, kobe's, kobes, kobs, kobus, kobza, koepke, koops, kopacz, kopas, kopec, kopecky, kopek, kopeks, kopischke, kopka, kopke, kopko, koppes, kops, kovac, kovach, kovach's, kovacic, kovacich, kovacik, kovack, kovacs, kovaks, kovich, kubacki, kubas, kubes, kubiak, kubic, kubica, kubicek, kubick, kubicki, kubik, kubis, kubisiak, kupek, kupiec, kupka