Accordion figures prominently in Arabic music--of course, it is a big part of Balkan music(though a lot of it is button, not keyboard).

My unexpected accordion find was years ago--I was recruiting a stage band for folkdance stage ensemble--we had a Ukraine wedding suite, and needed someone who knew the traditional wedding repertoire--there were no Ukranian ethnic enclaves in the particular city we were in (the nearest was a thousand miles away), and everyone had given up and decided to find a regular accordionist who was willing to learn the stuff from records. One day I was looking through the flea market shopper and saw an ad for a rock keyboardist who was looking for people to jam with--we talked and it turned out that he played accordion, "Not polkas or anything" he apologized, "My family are Ukranian, and I grew up playing at all the community weddings"--