I'd recommend adding chicks from a reputable hatchery or breeder, then quarantine isn't necessary.As I understand you don't have a quarantine facility, I recommend you not add new birds until you do.
My bigger concern seeing your set up however is you don't have coop space for more birds, and possibly not enough run space (though I don't know the measurements). Were there any plans to increase the size of coop and run? Integration, whether dealing with chicks or adults, favors extra space.