For a group of persons, or for a company or a partnership, Gentlemen, Dear Sirs, Dear Madams or Mesdames are used.
"Practical Grammar and Composition"
Thomas Wood
Look at the fine Madams in that broosh; they're as envious as can be.
"The Master of the Ceremonies"
George Manville Fenn
But mind this, my fine Madams, I may be only little Miss Clode at the library, but if you work any harm between you to those I love I'll have you both bundled neck and crop out of the place, or I'll know the reason why.
"The Master of the Ceremonies"
George Manville Fenn