Metropolises is the plural of metropolis, and for what I know, there aren't other plurals for that word.
Looking for metropolises at the Corpus of Contemporary American English and the British National Corpus, I get the following data:
(Corpus of Contemporary American English doesn't report any data under "non-academic" or "miscellaneous"; the scale is logarithmic.)
The higher number of times the word is found in the CoCA corpus is 31, which means a ratio of 0.38 per million.
Metropolises is used in sentences like the following:
I would refine this further to suggest that when experiences in small towns, ports, commercial cities, and industrial metropolises are compared, similarities far outweigh divergences across the country and that a broadly defined "Jewishkeit," or mixture of Jewish tradition, custom, values, and historical experience, exerted substantial influence over behavior.