I don't think that there are any underground haredi goups here in Israel that practice polygamy.  The takkanah against it is now universally accepted & is normative halakhah.  The ban on polygamy was never accepted by Jews in Yemen.  Even so, polygamy was extremely rare there.  There were a few instances of polygamous Yemenite Jews coming here.  The husbands were allowed to have two wives registered on their teudot zehut.  I think there are a few elderly such couples still around.  When they go, the institution of polygamy will go with them.

There have been cases here of haredim (and others) marryoing girls off at 15 or 16, which is illegal under Israeli law.

There have also been rare cases in which men have, under extraordinary circumstances, obtained rabbinical consent to take a second wife (100 rabbis must agree).

 L'chaim!

Oxartes

"But leave the Wise to wrangle,
and with me The Quarrel of the Universe let be:     
And, in some corner of the Hubbub coucht,     
Make Game of that which makes as much of Thee."
Omar Khayyam, "The Rubaiyat