Oligarchs rhymes with:
ballparks, benchmark's, benchmarks, birthmarks, bismarck's, caremark's, cellmark's, denmark's, deutschemark's, deutschemarks, earmarks, hallmark's, hallmarks, hartmarx, landmark's, landmarks, monarch's, monarchs, ozarks, pathmark's, patriarch's, patriarchs, raymark's, skylarks, southmark's, trademarks, watermarks, westmark's