Introducing a Cock

I curently have 17 laying hens and no Rooster , now i want chicks how long will it take to get fetile eggs or do i start? another coop with pullets and a cockeral or 2,or maybe get a male Leghorn and put a few of the RI reds hens in with him, i am planning on egg production for the neighborhood.once again since my hens are laying how long does it take for the fertile eggs to appear?Thanks Chris