The Irish male name Séadna is close. Not sure about Scottish Gaelic.
Sidney Carlyle's birth name is Sidney D. Carlyle.
Sidney Sheldon's birth name is Sidney Schechtel.
Sidney Torch's birth name is Sidney Torchinsky.
Sidney Arodin's birth name is Sidney Arnondrin.
Sidney Catlett's birth name is Sidney Catlett.
Sidney Moncrief's birth name is Sidney A. Moncrief.
Sidney Magal's birth name is Magalhes, Sidney.
Sidney Marion's birth name is Sidney Marienberg.
Sidney Kingsley's birth name is Sidney Kirshner.
Sidney Sidell's birth name is Sidney J. Sidell.
Sidney Soriano's birth name is Sidney Jean Soriano.
Sidney Ainsworth's birth name is Ainsworth, Charles Sidney.