Gradation rhymes with:
accommodation, backwardation, commendation, consolidation, degradation, depredation, fluoridation, foundation, fundacion, intimidation, inundation, invalidation, liquidation, oxidation, predation, recommendation, retardation, sedation, trepidation, validation
Gradation sounds like:
garden, gardena, gardenia, gardin, gardini, garduno, gardyne, garritano, garten, gartin, gartman, garton, gerdeman, giardina, giardini, giardino, giarratano, giordani, giordano, girardin, girten, girtman, girton, gordan, gordana, gorden, gordian, gordin, gordon, gortney, gorton, gourdine, graden, gradney, graduation, grattan, gratton, graydon, greetham, gretna, gritton, groden, grodin, groton, grutman, guardian, guardin, guardino, guertin, gwartney, gyration, gyrodyne