Mostar's rhymes with:
costars, costars, costars, ansgar's, armoires, bednarz, cesarz, costars, exemplars, finbar's, gancarz, lazarz, lenarz, lorimar's, polysar's, solarz, stolarz, tokarz, weglarz, zabar's
Mostar's sounds like:
master's, masters, masters', masterwork, masterworks, mastrich, mastrich's, mcdaris, mckitrick, mckittrick, mcwaters, mcwatters, megastores, meisters, mesothorax, minister's, ministers, ministers', ministries, ministry's, minstar's, misters, mistress, mistresses, mixtures, monasteries, monsters, monstrous, moonstruck, musketeers, musters, mysteries, mysterious