Help locating American marriage certificate

Can someone help me locate a marriage certificate in New York possibly Manhattan, for John Barrett born about 1870 in Cork, Ireland, and Ann Murray born about 1874 in Carlow, Ireland.

They appear on the 1905 census with their children Richard, Margaret and Terrance Barrett.

To date the majority of my research has been based in Ireland and the UK, so if anyone has any tips on the best place to find American certificates that would be great too.