How many countries...? I would also say that there are none.
Apparently the king of Tonga made a decree changing the numbering of the days, so that the people could "legally" call Sunday the seventh day of the week. It is strange, but professed SDA's in Tonga observe the Sabbath on Sunday. Perhaps this is the closest any country will ever come to recognizing the seventh day... but it is clear, I think, that this effort is an absurdity.